feat(ui): language persistence, theme fix, font/size settings, header quick-access

- Fix language not persisting after refresh: save locale in user_settings,
  set PARAGLIDE_LOCALE cookie from DB preference on server load
- Fix theme change not applying: context setter was mismatched (setTheme vs current)
- Add font family (system/serif/mono) and text size (sm/md/lg/xl) user settings
  stored in DB and applied via CSS custom properties
- Add theme color dots and language picker to desktop header for quick access
- Footer locale switcher now saves preference to DB before switching
- Remove change password section (OAuth-only, no password login)
- Fix active sessions piling up: reuse existing session on re-login via OAuth
- Extend speed step cycle to include 2.5× and 3.0× (matching profile slider)
- Replace plain checkbox with modern toggle switch for auto-next setting
- Fix catalogue status labels (ongoing/completed) to use translation keys
- Add font family and text size translation keys to all 5 locale files

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ui/src/lib/server/pocketbase.ts

@@ -55,6 +55,9 @@ export interface PBUserSettings {
 	voice: string;
 	speed: number;
 	theme?: string;
+	locale?: string;
+	font_family?: string;
+	font_size?: number;
 	updated?: string;
 }
 
@@ -803,7 +806,7 @@ export async function getSettings(
 
 export async function saveSettings(
 	sessionId: string,
-	settings: { autoNext: boolean; voice: string; speed: number; theme?: string },
+	settings: { autoNext: boolean; voice: string; speed: number; theme?: string; locale?: string; fontFamily?: string; fontSize?: number },
 	userId?: string
 ): Promise<void> {
 	const existing = await listOne<PBUserSettings & { id: string }>(
@@ -819,6 +822,9 @@ export async function saveSettings(
 		updated: new Date().toISOString()
 	};
 	if (settings.theme !== undefined) payload.theme = settings.theme;
+	if (settings.locale !== undefined) payload.locale = settings.locale;
+	if (settings.fontFamily !== undefined) payload.font_family = settings.fontFamily;
+	if (settings.fontSize !== undefined) payload.font_size = settings.fontSize;
 	if (userId) payload.user_id = userId;
 
 	if (existing) {