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/lib/api/chapters.test.ts

@@ -76,17 +76,17 @@ describe('chapters api client', () => {
         expect(result.page.total).toBeNull();
     });
 
-    it('getChapter hits /v1/mangas/{id}/chapters/{n}', async () => {
+    it('getChapter hits /v1/mangas/{id}/chapters/{chapter_id}', async () => {
         fetchSpy.mockResolvedValueOnce(ok(chapterFixture));
-        const c = await getChapter('m1', 1);
+        const c = await getChapter('m1', 'ch-uuid-1');
         expect(c).toEqual(chapterFixture);
         const url = fetchSpy.mock.calls[0][0] as string;
-        expect(url).toMatch(/\/v1\/mangas\/m1\/chapters\/1$/);
+        expect(url).toMatch(/\/v1\/mangas\/m1\/chapters\/ch-uuid-1$/);
     });
 
     it('getChapter surfaces 404 via ApiError.code', async () => {
         fetchSpy.mockResolvedValueOnce(envelope(404, 'not_found', 'not found'));
-        await expect(getChapter('m1', 99)).rejects.toMatchObject({
+        await expect(getChapter('m1', 'unknown-uuid')).rejects.toMatchObject({
             status: 404,
             code: 'not_found'
         });
@@ -143,10 +143,10 @@ describe('chapters api client', () => {
                 ]
             })
         );
-        const pages = await getChapterPages('m1', 1);
+        const pages = await getChapterPages('m1', 'ch-uuid-1');
         expect(pages).toHaveLength(1);
         expect(pages[0].storage_key).toContain('0001.png');
         const url = fetchSpy.mock.calls[0][0] as string;
-        expect(url).toMatch(/\/v1\/mangas\/m1\/chapters\/1\/pages$/);
+        expect(url).toMatch(/\/v1\/mangas\/m1\/chapters\/ch-uuid-1\/pages$/);
     });
 });