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>

frontend/src/lib/api/mangas.test.ts

@@ -60,14 +60,15 @@ describe('mangas api client', () => {
         expect(result.page).toEqual({ limit: 50, offset: 0, total: null });
     });
 
-    it('listMangas encodes search, limit, offset', async () => {
+    it('listMangas encodes search, limit, offset, sort', async () => {
         fetchSpy.mockResolvedValueOnce(ok(emptyPage()));
-        await listMangas({ search: 'one piece', limit: 10, offset: 20 });
+        await listMangas({ search: 'one piece', limit: 10, offset: 20, sort: 'title' });
         const url = fetchSpy.mock.calls[0][0] as string;
         expect(url).toMatch(/\/v1\/mangas\?/);
         expect(url).toContain('search=one+piece');
         expect(url).toContain('limit=10');
         expect(url).toContain('offset=20');
+        expect(url).toContain('sort=title');
     });
 
     it('createManga POSTs multipart with metadata to /v1/mangas', async () => {

frontend/src/lib/api/mangas.ts

@@ -1,9 +1,12 @@
 import { request, type Manga, type Page } from './client';
 
+export type MangaSort = 'recent' | 'title';
+
 export type ListOptions = {
     search?: string;
     limit?: number;
     offset?: number;
+    sort?: MangaSort;
 };
 
 export type MangasPage = {
@@ -16,6 +19,7 @@ export async function listMangas(opts: ListOptions = {}): Promise<MangasPage> {
     if (opts.search) params.set('search', opts.search);
     if (opts.limit != null) params.set('limit', String(opts.limit));
     if (opts.offset != null) params.set('offset', String(opts.offset));
+    if (opts.sort) params.set('sort', opts.sort);
     const qs = params.toString();
     return request<MangasPage>(`/v1/mangas${qs ? `?${qs}` : ''}`);
 }