feat(mangas): per-field sort options + direction toggle on the catalog (0.88.0)

Replace the two-option `ListSort` enum with an orthogonal sort field
(created/updated/title/author, default updated) and direction
(asc/desc, default desc). The catalog now defaults to last-updated-first
and lets the user order by any field in either direction.

Backend builds ORDER BY from the enums only (no injection seam), with a
NULLS-LAST author subquery and a stable id tie-break. Frontend adds a
direction toggle with per-field defaults (dates desc, text asc) and
labels (Newest/Oldest vs A->Z/Z->A), reusing SegmentedControl; URL state
omits the per-field defaults and validates on hydrate.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/api/mangas.rs

@@ -52,7 +52,9 @@ pub struct ListParams {
     #[serde(default)]
     pub offset: i64,
     #[serde(default)]
-    pub sort: repo::manga::ListSort,
+    pub sort: repo::manga::SortField,
+    #[serde(default)]
+    pub order: repo::manga::SortOrder,
 }
 
 fn default_limit() -> i64 {
@@ -105,6 +107,7 @@ async fn list(
         limit,
         offset,
         sort: params.sort,
+        order: params.order,
     };
     let (items, total) = repo::manga::list_cards(&state.db, &q).await?;
     Ok(Json(PagedResponse::with_total(items, limit, offset, total)))