feat: add sticky sidebar to chapter reader with ToC, progress, book info, and chapter nav

ui/src/routes/books/[slug]/chapters/[n]/+page.svelte

@@ -68,9 +68,10 @@
 		focusMode:   boolean;
 		playerStyle: PlayerStyle;
 		pageLines:   PageLines;
+		showSidebar: boolean;
 	}
 
-	const LAYOUT_KEY = 'reader_layout_v2';
+	const LAYOUT_KEY = 'reader_layout_v3';
 	const LINE_HEIGHTS:    Record<LineSpacing, number> = { compact: 1.55, normal: 1.85, relaxed: 2.2 };
 	const READ_WIDTHS:     Record<ReadWidth,   string> = { narrow: '58ch', normal: '72ch', wide: 'min(90ch, 100%)' };
 	/**
@@ -79,7 +80,7 @@
 	 * shorter so fewer lines fit per page; More (+4rem) grows it for more lines.
 	 */
 	const PAGE_LINES_OFFSET: Record<PageLines, string> = { less: '4rem', normal: '0rem', more: '-4rem' };
-	const DEFAULT_LAYOUT: LayoutPrefs = { readMode: 'scroll', lineSpacing: 'normal', readWidth: 'normal', paraStyle: 'spaced', focusMode: false, playerStyle: 'standard', pageLines: 'normal' };
+	const DEFAULT_LAYOUT: LayoutPrefs = { readMode: 'scroll', lineSpacing: 'normal', readWidth: 'normal', paraStyle: 'spaced', focusMode: false, playerStyle: 'standard', pageLines: 'normal', showSidebar: true };
 
 	function loadLayout(): LayoutPrefs {
 		if (!browser) return DEFAULT_LAYOUT;
@@ -466,6 +467,12 @@
 <div class="reading-progress" style="width: {scrollProgress * 100}%"></div>
 {/if}
 
+<!-- ── Two-column grid wrapper (sidebar activates at xl when enabled) ──────── -->
+<div class="{layout.showSidebar && !layout.focusMode ? 'xl:grid xl:grid-cols-[1fr_18rem] xl:gap-10 xl:items-start' : ''}">
+
+<!-- ── Main reading column ────────────────────────────────────────────────── -->
+<div>
+
 <!-- ── Top navigation (hidden in focus mode) ─────────────────────────────── -->
 {#if !layout.focusMode}
 <div class="flex items-center justify-between mb-8 gap-2">
@@ -864,6 +871,169 @@
 	</div>
 {/if}
 
+</div><!-- end main column -->
+
+<!-- ── Sidebar (xl+, hidden in focus mode, toggled via settings) ─────────── -->
+{#if layout.showSidebar && !layout.focusMode}
+<aside class="hidden xl:block">
+	<div class="sticky top-24 flex flex-col gap-4">
+
+		<!-- Card 1: Book cover + info -->
+		<div class="rounded-xl bg-(--color-surface-2) border border-(--color-border) overflow-hidden">
+			{#if data.book.cover}
+				<a href="/books/{data.book.slug}" tabindex="-1" aria-hidden="true">
+					<img
+						src={data.book.cover}
+						alt={data.book.title}
+						class="w-full aspect-[2/3] object-cover"
+					/>
+				</a>
+			{/if}
+			<div class="px-3 py-3 flex flex-col gap-2">
+				<a
+					href="/books/{data.book.slug}"
+					class="text-sm font-semibold text-(--color-text) hover:text-(--color-brand) transition-colors leading-snug line-clamp-2"
+				>
+					{data.book.title}
+				</a>
+				<div class="flex items-center gap-2 text-xs text-(--color-muted)">
+					<span class="tabular-nums">Ch. {data.chapter.number}</span>
+					{#if data.chapters.length > 0}
+						<span class="opacity-40">·</span>
+						<span class="tabular-nums">{data.chapters.length} chapters</span>
+					{/if}
+				</div>
+				{#if wordCount > 0}
+					<div class="flex items-center gap-2 text-xs text-(--color-muted)">
+						<span class="tabular-nums">{wordCount.toLocaleString()} words</span>
+						<span class="opacity-40">·</span>
+						<span>~{Math.max(1, Math.round(wordCount / 200))} min</span>
+					</div>
+				{/if}
+			</div>
+		</div>
+
+		<!-- Card 2: Reading progress -->
+		{#if data.chapters.length > 1}
+		{@const progressPct = Math.round((data.chapter.number / data.chapters.length) * 100)}
+		<div class="rounded-xl bg-(--color-surface-2) border border-(--color-border) px-4 py-3">
+			<p class="text-[10px] font-semibold text-(--color-muted) uppercase tracking-wider mb-2">Progress</p>
+			<div class="flex items-center justify-between text-xs text-(--color-muted) mb-1.5">
+				<span>Chapter {data.chapter.number} of {data.chapters.length}</span>
+				<span class="tabular-nums font-medium text-(--color-brand)">{progressPct}%</span>
+			</div>
+			<div class="h-1.5 rounded-full bg-(--color-surface-3) overflow-hidden">
+				<div
+					class="h-full rounded-full bg-(--color-brand) transition-all"
+					style="width: {progressPct}%"
+				></div>
+			</div>
+			{#if layout.readMode === 'scroll' && scrollProgress > 0}
+				<div class="mt-2 flex items-center gap-2 text-xs text-(--color-muted)">
+					<span>Page scroll</span>
+					<div class="flex-1 h-1 rounded-full bg-(--color-surface-3) overflow-hidden">
+						<div
+							class="h-full rounded-full bg-(--color-brand)/50 transition-all"
+							style="width: {Math.round(scrollProgress * 100)}%"
+						></div>
+					</div>
+					<span class="tabular-nums">{Math.round(scrollProgress * 100)}%</span>
+				</div>
+			{/if}
+			{#if layout.readMode === 'paginated' && totalPages > 1}
+				<div class="mt-2 flex items-center gap-2 text-xs text-(--color-muted)">
+					<span>Page</span>
+					<div class="flex-1 h-1 rounded-full bg-(--color-surface-3) overflow-hidden">
+						<div
+							class="h-full rounded-full bg-(--color-brand)/50 transition-all"
+							style="width: {Math.round(((pageIndex + 1) / totalPages) * 100)}%"
+						></div>
+					</div>
+					<span class="tabular-nums">{pageIndex + 1}/{totalPages}</span>
+				</div>
+			{/if}
+		</div>
+		{/if}
+
+		<!-- Card 3: Chapter ToC -->
+		{#if data.chapters.length > 0}
+		{@const tocChapters = data.chapters}
+		{@const currentIdx = tocChapters.findIndex(c => c.number === data.chapter.number)}
+		{@const windowStart = Math.max(0, currentIdx - 3)}
+		{@const windowEnd = Math.min(tocChapters.length, windowStart + 10)}
+		<div class="rounded-xl bg-(--color-surface-2) border border-(--color-border) overflow-hidden">
+			<div class="flex items-center justify-between px-3 py-2.5 border-b border-(--color-border)">
+				<p class="text-[10px] font-semibold text-(--color-muted) uppercase tracking-wider">Chapters</p>
+				<a
+					href="/books/{data.book.slug}/chapters"
+					class="text-[10px] text-(--color-brand) hover:underline"
+				>All {tocChapters.length}</a>
+			</div>
+			<div class="flex flex-col divide-y divide-(--color-border)/50 max-h-64 overflow-y-auto">
+				{#each tocChapters.slice(windowStart, windowEnd) as ch}
+					{@const isCurrent = ch.number === data.chapter.number}
+					<a
+						href="/books/{data.book.slug}/chapters/{ch.number}"
+						class="flex items-start gap-2 px-3 py-2 text-xs transition-colors
+							{isCurrent
+								? 'bg-(--color-brand)/10 text-(--color-brand) font-semibold'
+								: 'text-(--color-muted) hover:text-(--color-text) hover:bg-(--color-surface-3)'}"
+					>
+						<span class="shrink-0 tabular-nums w-6 text-right opacity-60">{ch.number}</span>
+						<span class="truncate leading-snug">{ch.title || `Chapter ${ch.number}`}</span>
+					</a>
+				{/each}
+			</div>
+		</div>
+		{/if}
+
+		<!-- Card 4: Chapter navigation -->
+		<div class="rounded-xl bg-(--color-surface-2) border border-(--color-border) px-3 py-3 flex flex-col gap-2">
+			<p class="text-[10px] font-semibold text-(--color-muted) uppercase tracking-wider mb-0.5">Navigate</p>
+			{#if data.prev}
+				<a
+					href="/books/{data.book.slug}/chapters/{data.prev}"
+					class="flex items-center gap-2 px-3 py-2 rounded-lg text-xs text-(--color-muted) hover:text-(--color-text) hover:bg-(--color-surface-3) transition-colors"
+				>
+					<svg class="w-3.5 h-3.5 shrink-0" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+						<path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M15 19l-7-7 7-7"/>
+					</svg>
+					<span class="truncate">Chapter {data.prev}</span>
+				</a>
+			{:else}
+				<span class="flex items-center gap-2 px-3 py-2 text-xs text-(--color-muted)/30">
+					<svg class="w-3.5 h-3.5 shrink-0" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+						<path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M15 19l-7-7 7-7"/>
+					</svg>
+					First chapter
+				</span>
+			{/if}
+			{#if data.next}
+				<a
+					href="/books/{data.book.slug}/chapters/{data.next}"
+					class="flex items-center gap-2 px-3 py-2 rounded-lg text-xs text-(--color-brand) bg-(--color-brand)/10 hover:bg-(--color-brand)/20 transition-colors font-medium"
+				>
+					<svg class="w-3.5 h-3.5 shrink-0" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+						<path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9 5l7 7-7 7"/>
+					</svg>
+					<span class="truncate">Chapter {data.next}</span>
+				</a>
+			{:else}
+				<span class="flex items-center gap-2 px-3 py-2 text-xs text-(--color-muted)/30">
+					<svg class="w-3.5 h-3.5 shrink-0" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+						<path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9 5l7 7-7 7"/>
+					</svg>
+					Last chapter
+				</span>
+			{/if}
+		</div>
+
+	</div>
+</aside>
+{/if}
+
+</div><!-- end grid wrapper -->
+
 <!-- ── Scroll mode floating nav buttons ──────────────────────────────────── -->
 {#if layout.readMode === 'scroll' && !layout.focusMode}
 {@const atTop = scrollProgress <= 0.01}
@@ -1227,6 +1397,17 @@
 					<span class="text-(--color-muted) text-[11px]">{layout.focusMode ? 'On — audio & nav hidden' : 'Off'}</span>
 				</button>
 
+				<button
+					type="button"
+					onclick={() => setLayout('showSidebar', !layout.showSidebar)}
+					class="w-full flex items-center justify-between px-3 py-2.5 text-xs font-medium transition-colors
+						{layout.showSidebar ? 'text-(--color-brand)' : 'text-(--color-text) hover:text-(--color-brand)'}"
+					aria-pressed={layout.showSidebar}
+				>
+					<span>Sidebar</span>
+					<span class="text-(--color-muted) text-[11px]">{layout.showSidebar ? 'On — ToC, progress & nav' : 'Off'}</span>
+				</button>
+
 			</div>
 		</div>