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/routes/+page.svelte

@@ -1,9 +1,11 @@
 <script lang="ts">
     import { onMount } from 'svelte';
-    import { listMangas, type Manga } from '$lib/api/mangas';
+    import { listMangas, type Manga, type MangaSort } from '$lib/api/mangas';
 
     let mangas: Manga[] = $state([]);
     let search = $state('');
+    let sort: MangaSort = $state('recent');
+    let total: number | null = $state(null);
     let loading = $state(true);
     let error: string | null = $state(null);
 
@@ -11,7 +13,12 @@
         loading = true;
         error = null;
         try {
-            mangas = (await listMangas({ search: search.trim() || undefined })).items;
+            const result = await listMangas({
+                search: search.trim() || undefined,
+                sort
+            });
+            mangas = result.items;
+            total = result.page.total;
         } catch (e) {
             error = (e as Error).message;
         } finally {
@@ -19,6 +26,10 @@
         }
     }
 
+    function onSortChange() {
+        load();
+    }
+
     onMount(load);
 </script>
 
@@ -30,6 +41,7 @@
         load();
     }}
     action="javascript:void(0)"
+    class="controls"
 >
     <input
         type="search"
@@ -37,6 +49,13 @@
         placeholder="Search by title or author"
         data-testid="search-input"
     />
+    <label>
+        Sort
+        <select bind:value={sort} onchange={onSortChange} data-testid="sort-select">
+            <option value="recent">Recent</option>
+            <option value="title">Title (A→Z)</option>
+        </select>
+    </label>
     <button type="submit">Search</button>
 </form>
 
@@ -47,6 +66,11 @@
 {:else if mangas.length === 0}
     <p data-testid="empty">No mangas yet. <a href="/upload">Upload one</a>.</p>
 {:else}
+    {#if total !== null}
+        <p class="count" data-testid="manga-total">
+            Showing {mangas.length} of {total}
+        </p>
+    {/if}
     <ul data-testid="manga-list">
         {#each mangas as m (m.id)}
             <li>
@@ -56,3 +80,21 @@
         {/each}
     </ul>
 {/if}
+
+<style>
+    .controls {
+        display: flex;
+        gap: 0.5rem;
+        align-items: center;
+        flex-wrap: wrap;
+    }
+    .controls label {
+        display: flex;
+        align-items: center;
+        gap: 0.25rem;
+    }
+    .count {
+        color: #777;
+        margin: 0.5rem 0;
+    }
+</style>