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>

backend/src/api/chapters.rs

@@ -26,9 +26,9 @@ use crate::upload::{parse_image, UploadedImage};
 pub fn routes() -> Router<AppState> {
     Router::new()
         .route("/mangas/:manga_id/chapters", get(list).post(create))
-        .route("/mangas/:manga_id/chapters/:number", get(get_one))
+        .route("/mangas/:manga_id/chapters/:chapter_id", get(get_one))
         .route(
-            "/mangas/:manga_id/chapters/:number/pages",
+            "/mangas/:manga_id/chapters/:chapter_id/pages",
             get(list_pages),
         )
 }
@@ -60,10 +60,10 @@ async fn list(
 
 async fn get_one(
     State(state): State<AppState>,
-    Path((manga_id, number)): Path<(Uuid, i32)>,
+    Path((manga_id, chapter_id)): Path<(Uuid, Uuid)>,
 ) -> AppResult<Json<Chapter>> {
     repo::manga::get(&state.db, manga_id).await?;
-    let chapter = repo::chapter::find_by_manga_and_number(&state.db, manga_id, number)
+    let chapter = repo::chapter::find_by_id_in_manga(&state.db, manga_id, chapter_id)
         .await?
         .ok_or(AppError::NotFound)?;
     Ok(Json(chapter))
@@ -164,10 +164,10 @@ struct PagesResponse {
 
 async fn list_pages(
     State(state): State<AppState>,
-    Path((manga_id, number)): Path<(Uuid, i32)>,
+    Path((manga_id, chapter_id)): Path<(Uuid, Uuid)>,
 ) -> AppResult<Json<PagesResponse>> {
     repo::manga::get(&state.db, manga_id).await?;
-    let chapter = repo::chapter::find_by_manga_and_number(&state.db, manga_id, number)
+    let chapter = repo::chapter::find_by_id_in_manga(&state.db, manga_id, chapter_id)
         .await?
         .ok_or(AppError::NotFound)?;
     let pages = repo::page::list_for_chapter(&state.db, chapter.id).await?;