feat: route reader by chapter id, allow duplicate-numbered chapters (0.24.0)

Real-world sources publish multiple chapters at the same number:
different scanlators ("Ch.52 from bloomingdale" + "Ch.52 from mina"),
translator notices and farewells, alt-translations. The (manga_id,
number) UNIQUE constraint from 0001 silently collapsed all of those
into a single row via the upsert path in repo::crawler. Migration 0013
drops the constraint; sync_manga_chapters now plain-INSERTs each
SourceChapterRef so every parsed chapter survives as its own row.

Identity moves from the (manga_id, number) tuple to the chapter UUID:

- `GET /api/v1/mangas/:manga_id/chapters/:chapter_id` (replaces :number)
- `GET /api/v1/mangas/:manga_id/chapters/:chapter_id/pages`
- `repo::chapter::find_by_id_in_manga` (replaces find_by_manga_and_number)
- Frontend reader route renamed to `/manga/[id]/chapter/[chapter_id]`
- Chapter links throughout (manga page list, continue-reading CTA,
  reader prev/next, history rows, bookmark cards) use chapter.id
- API clients getChapter/getChapterPages take a chapter id string

read_progress + bookmarks already FK chapter_id; they only enrich with
chapter_number for display, which is preserved.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/routes/profile/history/+page.svelte

@@ -60,8 +60,8 @@
                 {#each progress as p (p.manga_id)}
                     <li class="entry">
                         <a
-                            href={p.chapter_number != null
-                                ? `/manga/${p.manga_id}/chapter/${p.chapter_number}`
+                            href={p.chapter_id != null
+                                ? `/manga/${p.manga_id}/chapter/${p.chapter_id}`
                                 : `/manga/${p.manga_id}`}
                             class="cover-link"
                             tabindex="-1"
@@ -89,9 +89,9 @@
                                 {p.manga_title}
                             </a>
                             <span class="target">
-                                {#if p.chapter_number != null}
+                                {#if p.chapter_id != null && p.chapter_number != null}
                                     <a
-                                        href="/manga/{p.manga_id}/chapter/{p.chapter_number}"
+                                        href="/manga/{p.manga_id}/chapter/{p.chapter_id}"
                                     >
                                         Continue Ch. {p.chapter_number}{#if p.page > 1} — page {p.page}{/if}
                                     </a>
@@ -185,7 +185,7 @@
                             <div class="meta">
                                 <a href="/manga/{u.manga_id}" class="title">{u.manga_title}</a>
                                 <span class="target">
-                                    <a href="/manga/{u.manga_id}/chapter/{u.chapter.number}">
+                                    <a href="/manga/{u.manga_id}/chapter/{u.chapter.id}">
                                         Chapter {u.chapter.number}{#if u.chapter.title}: {u.chapter.title}{/if}
                                     </a>
                                     <span class="muted">({u.chapter.page_count} pages)</span>