fix(mangas): address review on sort feature — alias, index, validation, a11y

Backend
- sort=recent stays a back-compat alias for created (parse_sort); invalid
  sort/order now return the structured 422 envelope instead of plain-text 400
- per-field default direction on omitted order (dates desc, text asc), matching
  the frontend so a bare ?sort=<field> reads the same in UI and API
- migration 0033: index mangas(updated_at DESC, id) backing the default sort
  and its id tie-break; NULLS LAST now applied only to the nullable author key
- tests: recent alias, per-field default (title+author), invalid-value 422,
  and a tie-break test that pins ordering by ascending id (mutation-verified)

Frontend
- pure sort helpers extracted to $lib/mangaSort with unit tests; coerceSort
  honors the recent alias so pasted/legacy URLs resolve to the same field
- SegmentedControl: roving tabindex + arrow/Home/End keyboard nav, anchored on
  focus so rapid keypresses don't stick
- UX: visible "Direction" labels (desktop + mobile), mobile sort-sheet section
  headings and a "Done" button; README sort/order contract updated

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/api/mangas.rs

@@ -51,16 +51,58 @@ pub struct ListParams {
     pub limit: i64,
     #[serde(default)]
     pub offset: i64,
+    /// Sort field: `created`, `updated` (default), `title`, or `author`.
+    /// Also accepts the legacy `recent` alias (== `created`). Anything
+    /// else → 422.
     #[serde(default)]
-    pub sort: repo::manga::SortField,
+    pub sort: Option<String>,
+    /// `asc` or `desc`. Omitted → the field's natural default
+    /// (dates `desc`, text `asc`). Anything else → 422.
     #[serde(default)]
-    pub order: repo::manga::SortOrder,
+    pub order: Option<String>,
 }
 
 fn default_limit() -> i64 {
     50
 }
 
+/// Parse the `sort` wire value into a [`repo::manga::SortField`]. Validation
+/// and the legacy `recent` alias live here (not in serde) so unknown values
+/// return the structured 422 envelope rather than axum's plain-text
+/// `QueryRejection`, matching the rest of this handler's filters.
+fn parse_sort(raw: Option<&str>) -> AppResult<repo::manga::SortField> {
+    use repo::manga::SortField;
+    match raw.map(str::trim) {
+        None | Some("") | Some("updated") => Ok(SortField::Updated),
+        // `recent` was the pre-0.88 name for "newest created first"; keep it
+        // as an alias so existing bots/scripts don't break.
+        Some("created") | Some("recent") => Ok(SortField::Created),
+        Some("title") => Ok(SortField::Title),
+        Some("author") => Ok(SortField::Author),
+        Some(other) => Err(AppError::ValidationFailed {
+            message: format!(
+                "sort must be one of created, updated, title, author (got {other:?})"
+            ),
+            details: json!({ "sort": "invalid" }),
+        }),
+    }
+}
+
+/// Parse the `order` wire value. `None` means the client omitted it, so the
+/// caller applies the field's natural default. An explicit unknown value → 422.
+fn parse_order(raw: Option<&str>) -> AppResult<Option<repo::manga::SortOrder>> {
+    use repo::manga::SortOrder;
+    match raw.map(str::trim) {
+        None | Some("") => Ok(None),
+        Some("asc") => Ok(Some(SortOrder::Asc)),
+        Some("desc") => Ok(Some(SortOrder::Desc)),
+        Some(other) => Err(AppError::ValidationFailed {
+            message: format!("order must be 'asc' or 'desc' (got {other:?})"),
+            details: json!({ "order": "invalid" }),
+        }),
+    }
+}
+
 fn parse_uuid_csv(field: &str, raw: Option<&str>) -> AppResult<Vec<Uuid>> {
     let Some(raw) = raw else { return Ok(Vec::new()) };
     let mut out = Vec::new();
@@ -96,6 +138,10 @@ async fn list(
             Some(s.to_string())
         }
     };
+    let sort = parse_sort(params.sort.as_deref())?;
+    // Omitted `order` falls back to the field's natural direction, so a bare
+    // `?sort=title` reads A→Z just like the UI shows it.
+    let order = parse_order(params.order.as_deref())?.unwrap_or_else(|| sort.default_order());
     let q = repo::manga::ListQuery {
         search: params.search.filter(|s| !s.trim().is_empty()),
         status,
@@ -106,8 +152,8 @@ async fn list(
         cw_exclude: crate::api::page_tags::parse_warnings_csv(params.cw_exclude.as_deref())?,
         limit,
         offset,
-        sort: params.sort,
-        order: params.order,
+        sort,
+        order,
     };
     let (items, total) = repo::manga::list_cards(&state.db, &q).await?;
     Ok(Json(PagedResponse::with_total(items, limit, offset, total)))