feat: pg_trgm search, sort options, populated total count

Backend:
- Migration 0005_search.sql enables pg_trgm and adds GIN indexes
  (gin_trgm_ops) on mangas.title and on mangas.author (partial, WHERE
  author IS NOT NULL).
- repo::manga::list keeps the existing substring (ILIKE) clause and
  adds the `%` operator on title + author so the search tolerates typos
  ('narto' → 'Naruto'). Both branches share the trgm index. A second
  count(*) query (same WHERE clause, indexed) yields the total without
  scanning twice in any meaningful sense.
- New ListSort enum (Recent / Title) interpolated into ORDER BY from a
  hard-coded match — never from request input, so the format!() is not
  a SQL-injection seam. Default stays Recent (created_at DESC).
- api::mangas accepts `?sort=recent|title` (snake_case) via serde and
  returns `page.total` as a number instead of null.
- api::pagination::PagedResponse gains a `with_total` constructor.

Backend coverage in tests/api_mangas.rs (4 new cases plus the existing
list_is_empty_initially updated to assert total: 0):
- list_returns_total_count_independent_of_pagination — limit=2 with 3
  rows returns 2 items and total=3.
- search_via_trigram_tolerates_typos — `?search=narto` finds Naruto.
- list_sort_title_orders_alphabetically — three out-of-order inserts
  come back A→Z.
- search_reflects_filtered_total — search narrows total to 1.

Frontend:
- lib/api/mangas.ts gains a `MangaSort` type and threads `sort` through
  listMangas's query-string builder.
- Home page renders a "Sort" select (Recent / Title A→Z) that re-runs
  the list query, and shows "Showing N of M" when total is present.

Lockstep version bump to 0.8.0.

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

backend/src/api/mangas.rs

@@ -28,6 +28,8 @@ pub struct ListParams {
     pub limit: i64,
     #[serde(default)]
     pub offset: i64,
+    #[serde(default)]
+    pub sort: repo::manga::ListSort,
 }
 
 fn default_limit() -> i64 {
@@ -44,9 +46,10 @@ async fn list(
         search: params.search.filter(|s| !s.trim().is_empty()),
         limit,
         offset,
+        sort: params.sort,
     };
-    let items = repo::manga::list(&state.db, &q).await?;
-    Ok(Json(PagedResponse::new(items, limit, offset)))
+    let (items, total) = repo::manga::list(&state.db, &q).await?;
+    Ok(Json(PagedResponse::with_total(items, limit, offset, total)))
 }
 
 async fn get_one(

backend/src/api/pagination.rs

@@ -27,4 +27,11 @@ impl<T> PagedResponse<T> {
             page: PageInfo { limit, offset, total: None },
         }
     }
+
+    pub fn with_total(items: Vec<T>, limit: i64, offset: i64, total: i64) -> Self {
+        Self {
+            items,
+            page: PageInfo { limit, offset, total: Some(total) },
+        }
+    }
 }