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/lib/api/chapters.test.ts

@@ -7,7 +7,7 @@ import {
     afterEach,
     type MockInstance
 } from 'vitest';
-import { listChapters, getChapter } from './chapters';
+import { listChapters, getChapter, getChapterPages } from './chapters';
 
 function ok(body: unknown): Response {
     return new Response(JSON.stringify(body), {
@@ -86,4 +86,25 @@ describe('chapters api client', () => {
             code: 'not_found'
         });
     });
+
+    it('getChapterPages unwraps the {pages} envelope into the array', async () => {
+        fetchSpy.mockResolvedValueOnce(
+            ok({
+                pages: [
+                    {
+                        id: 'p1',
+                        chapter_id: 'c1',
+                        page_number: 1,
+                        storage_key: 'mangas/m1/chapters/c1/pages/0001.png',
+                        content_type: 'image/png'
+                    }
+                ]
+            })
+        );
+        const pages = await getChapterPages('m1', 1);
+        expect(pages).toHaveLength(1);
+        expect(pages[0].storage_key).toContain('0001.png');
+        const url = fetchSpy.mock.calls[0][0] as string;
+        expect(url).toMatch(/\/v1\/mangas\/m1\/chapters\/1\/pages$/);
+    });
 });

frontend/src/lib/api/chapters.ts

@@ -37,3 +37,21 @@ export async function getChapter(mangaId: string, number: number): Promise<Chapt
         `/v1/mangas/${encodeURIComponent(mangaId)}/chapters/${number}`
     );
 }
+
+export type ChapterPage = {
+    id: string;
+    chapter_id: string;
+    page_number: number;
+    storage_key: string;
+    content_type: string;
+};
+
+export async function getChapterPages(
+    mangaId: string,
+    number: number
+): Promise<ChapterPage[]> {
+    const r = await request<{ pages: ChapterPage[] }>(
+        `/v1/mangas/${encodeURIComponent(mangaId)}/chapters/${number}/pages`
+    );
+    return r.pages;
+}

frontend/src/lib/api/client.ts

@@ -3,6 +3,15 @@
 
 const BASE = import.meta.env?.VITE_API_BASE ?? '/api';
 
+/**
+ * Builds an absolute URL to the streaming `/files/{key}` endpoint so
+ * components can use it directly in `<img src>` etc., without
+ * reconstructing the API base in each call site.
+ */
+export function fileUrl(key: string): string {
+    return `${BASE}/v1/files/${key}`;
+}
+
 export class ApiError extends Error {
     constructor(
         public readonly status: number,