bugfix: bookmark chapter links use chapter number, not UUID

The reader route is keyed on chapter number (URL `/manga/{id}/chapter/{n}`,
loaded via `Number(params.n)`), but the bookmarks list was building
hrefs from `chapter_id` (a UUID). Following any chapter bookmark
produced a NaN load on the reader page.

Fix at the API layer so every consumer of /me/bookmarks gets the
information without a follow-up round-trip per bookmark.

- domain::BookmarkSummary: new type, `Bookmark` plus
  `chapter_number: Option<i32>`. Populated by a LEFT JOIN on chapters
  so manga-level bookmarks come back with `chapter_number = null` and
  chapter-level ones get the value. `Bookmark` itself stays minimal
  for POST / DELETE responses.
- repo::bookmark::list_for_user returns Vec<BookmarkSummary>.
- api::bookmarks::list_me returns PagedResponse<BookmarkSummary>.
- Frontend `Bookmark` type carries an optional `chapter_number`.
- /bookmarks page builds `/manga/{manga_id}/chapter/{chapter_number}`
  for chapter bookmarks, falling back to the manga overview if the
  chapter has been deleted out from under the bookmark (chapter_id is
  ON DELETE SET NULL, so this is a real edge case).

New test asserts both branches of the JOIN: a chapter-level bookmark
comes back with the right chapter_number and page, a manga-level one
has a null chapter_number.

Lockstep version bump to 0.9.2.

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

backend/tests/api_bookmarks.rs

@@ -221,6 +221,81 @@ async fn list_me_requires_authentication(pool: PgPool) {
     assert_eq!(resp.status(), StatusCode::UNAUTHORIZED);
 }
 
+#[sqlx::test(migrations = "./migrations")]
+async fn list_me_enriches_chapter_bookmarks_with_chapter_number(pool: PgPool) {
+    let h = common::harness(pool.clone());
+    let (_, cookie) = common::register_user(&h.app).await;
+    let manga_id = common::seed_manga_via_api(&h.app, &cookie, "Berserk").await;
+    // Seed a chapter directly so we know its number without uploading pages.
+    mangalord::repo::chapter::create(&pool, manga_id, 7, Some("The Brand"))
+        .await
+        .unwrap();
+    // Look up its id so we can bookmark it.
+    let chapter_id: Uuid = sqlx::query_scalar(
+        "SELECT id FROM chapters WHERE manga_id = $1 AND number = $2",
+    )
+    .bind(manga_id)
+    .bind(7_i32)
+    .fetch_one(&pool)
+    .await
+    .unwrap();
+
+    // Bookmark the chapter at page 4.
+    let resp = h
+        .app
+        .clone()
+        .oneshot(common::post_json_with_cookie(
+            "/api/v1/bookmarks",
+            json!({
+                "manga_id": manga_id.to_string(),
+                "chapter_id": chapter_id.to_string(),
+                "page": 4
+            }),
+            &cookie,
+        ))
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), StatusCode::CREATED);
+
+    // Also bookmark the manga at the manga level — chapter_number must
+    // come back null for it, populated for the chapter one.
+    let _ = h
+        .app
+        .clone()
+        .oneshot(common::post_json_with_cookie(
+            "/api/v1/bookmarks",
+            json!({ "manga_id": manga_id.to_string() }),
+            &cookie,
+        ))
+        .await
+        .unwrap();
+
+    let resp = h
+        .app
+        .oneshot(common::get_with_cookie("/api/v1/me/bookmarks", &cookie))
+        .await
+        .unwrap();
+    let body = common::body_json(resp).await;
+    let items = body["items"].as_array().unwrap();
+    assert_eq!(items.len(), 2);
+
+    let chapter_bookmark = items
+        .iter()
+        .find(|b| !b["chapter_id"].is_null())
+        .expect("chapter-level bookmark present");
+    assert_eq!(chapter_bookmark["chapter_number"], 7);
+    assert_eq!(chapter_bookmark["page"], 4);
+
+    let manga_bookmark = items
+        .iter()
+        .find(|b| b["chapter_id"].is_null())
+        .expect("manga-level bookmark present");
+    assert!(
+        manga_bookmark["chapter_number"].is_null(),
+        "manga-level bookmark must have a null chapter_number"
+    );
+}
+
 #[sqlx::test(migrations = "./migrations")]
 async fn list_me_returns_paged_envelope(pool: PgPool) {
     let h = common::harness(pool);