feat: add avatars to comments (web + iOS) with replies, delete, sort, and crop fix

- Batch-resolve avatar presign URLs server-side in GET /api/comments/[slug];
  returns avatarUrls map alongside comments and myVotes
- CommentsSection.svelte: show avatar image or initials fallback (24px top-level,
  20px replies) next to each comment/reply username
- iOS CommentsResponse gains avatarUrls field; CommentsViewModel stores and
  populates it on load; CommentRow renders AsyncImage with initials fallback
- Also includes: comment replies (1-level nesting), delete, sort (Top/New),
  parent_id schema migration, and AvatarCropModal cropperjs fix

ui/src/routes/books/[slug]/+page.server.ts

@@ -43,7 +43,9 @@ export const load: PageServerLoad = async ({ params, locals }) => {
 			inLib: true,
 			saved,
 			lastChapter: progress?.chapter ?? null,
-			isAdmin: locals.user?.role === 'admin'
+			isAdmin: locals.user?.role === 'admin',
+			isLoggedIn: !!locals.user,
+			currentUserId: locals.user?.id ?? ''
 		};
 	}
 
@@ -93,7 +95,9 @@ export const load: PageServerLoad = async ({ params, locals }) => {
 			inLib: preview.in_lib,
 			saved: false,
 			lastChapter: null,
-			isAdmin: locals.user?.role === 'admin'
+			isAdmin: locals.user?.role === 'admin',
+			isLoggedIn: !!locals.user,
+			currentUserId: locals.user?.id ?? ''
 		};
 	} catch (e) {
 		if (e instanceof Error && 'status' in e) throw e;

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

@@ -528,4 +528,4 @@
 </div>
 
 <!-- ══════════════════════════════════════════════════ Comments ══ -->
-<CommentsSection slug={data.book.slug} isLoggedIn={true} />
+<CommentsSection slug={data.book.slug} isLoggedIn={data.isLoggedIn} currentUserId={data.currentUserId} />