feat: streaming files endpoint + reader pages + chapter pages metadata

Backend:
- Migration 0003_pages.sql adds a `pages` table (id, chapter_id,
  page_number, storage_key, content_type) with a unique (chapter_id,
  page_number). New table because chapter pages can have different MIME
  types per page; reconstructing keys from a single template would
  break the moment a chapter mixes png and jpg pages.
- `domain::Page` + `repo::page` (create + list_for_chapter).
- The chapter upload handler now inserts one page row per part as it
  writes the bytes to storage.
- GET /api/v1/mangas/{id}/chapters/{n}/pages returns `{pages: [...]}`
  with the storage_key clients need to construct image URLs. 404 if
  the manga or chapter doesn't exist; reads are public.

Storage trait grows `get_stream(&str) -> StreamingFile` returning a
`Pin<Box<dyn Stream<Item = io::Result<Bytes>> + Send>>` + size. The
local backend implements via `tokio::fs::File` + `tokio_util::io::
ReaderStream` with a 64 KiB chunk size. GET /api/v1/files/*key now
streams via `axum::body::Body::from_stream` instead of buffering — the
test asserts a 200 KiB file emits >1 frame end-to-end through the
router.

Frontend:
- lib/api/client.ts gains `fileUrl(key)` so components don't
  reconstruct the `/api/v1/files/...` path manually.
- lib/api/chapters.ts gains `ChapterPage` type + `getChapterPages` (the
  type is named ChapterPage to avoid colliding with `Page` from
  client.ts, which is the pagination envelope).
- /manga/[id]/+page.svelte: overview with cover, title, author,
  description, chapter list, and a disabled bookmark control (real
  bookmarking lands in feat/bookmarks). Responsive at 640 px.
- /manga/[id]/chapter/[n]/+page.svelte: paginated reader. Current page
  loads eagerly; next page is preloaded in a hidden img so navigation
  feels instant. Keyboard handler maps ArrowRight/j/Space → next,
  ArrowLeft/k → prev, Home/End → first/last; skips when the user is
  typing in an input. Focus ring on the prev/next buttons.
- SSR is disabled on both routes via `export const ssr = false` so the
  client-only fetch flow doesn't need to be replicated server-side; the
  routes are interactive features, not SEO surfaces.
- E2E (e2e/reader.spec.ts): overview shows the title/cover/chapter
  list; reader pages through three pages via ArrowRight, j, k, and
  ArrowLeft, and the preload img holds the page-2 src on initial load.

Lockstep version bump to 0.6.0.

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

frontend/src/routes/manga/[id]/+page.svelte

@@ -0,0 +1,101 @@
+<script lang="ts">
+    import { fileUrl } from '$lib/api/client';
+
+    let { data } = $props();
+    const manga = $derived(data.manga);
+    const chapters = $derived(data.chapters);
+</script>
+
+<svelte:head>
+    <title>{manga.title} — Mangalord</title>
+</svelte:head>
+
+<article>
+    <header class="overview">
+        {#if manga.cover_image_path}
+            <img
+                src={fileUrl(manga.cover_image_path)}
+                alt="{manga.title} cover"
+                class="cover"
+                loading="eager"
+                data-testid="manga-cover"
+            />
+        {/if}
+        <div class="meta">
+            <h1 data-testid="manga-title">{manga.title}</h1>
+            {#if manga.author}
+                <p class="author" data-testid="manga-author">by {manga.author}</p>
+            {/if}
+            {#if manga.description}
+                <p class="description" data-testid="manga-description">{manga.description}</p>
+            {/if}
+            <button
+                type="button"
+                class="bookmark"
+                disabled
+                aria-disabled="true"
+                title="Bookmarking lands in feat/bookmarks"
+                data-testid="bookmark-placeholder"
+            >
+                ☆ Bookmark
+            </button>
+        </div>
+    </header>
+
+    <section aria-label="chapters">
+        <h2>Chapters</h2>
+        {#if chapters.length === 0}
+            <p data-testid="chapters-empty">No chapters yet.</p>
+        {:else}
+            <ol class="chapter-list" data-testid="chapter-list">
+                {#each chapters as c (c.id)}
+                    <li>
+                        <a href="/manga/{manga.id}/chapter/{c.number}">
+                            Chapter {c.number}{#if c.title}: {c.title}{/if}
+                        </a>
+                        <span class="pages">({c.page_count} pages)</span>
+                    </li>
+                {/each}
+            </ol>
+        {/if}
+    </section>
+</article>
+
+<style>
+    .overview {
+        display: grid;
+        grid-template-columns: minmax(0, 200px) 1fr;
+        gap: 1rem;
+        align-items: start;
+    }
+    @media (max-width: 640px) {
+        .overview {
+            grid-template-columns: 1fr;
+        }
+    }
+    .cover {
+        width: 100%;
+        height: auto;
+        border-radius: 4px;
+    }
+    .meta h1 {
+        margin: 0 0 0.5rem;
+    }
+    .author {
+        color: #555;
+        margin: 0 0 0.75rem;
+    }
+    .description {
+        white-space: pre-wrap;
+    }
+    .bookmark {
+        margin-top: 0.5rem;
+    }
+    .chapter-list {
+        padding-left: 1.5rem;
+    }
+    .pages {
+        color: #777;
+        margin-left: 0.5rem;
+    }
+</style>