feat: edit existing manga metadata (0.31.0)

Adds PUT /mangas/:id/cover (multipart) and DELETE /mangas/:id/cover so
covers can be replaced or cleared after creation, and wires a dedicated
/manga/[id]/edit SvelteKit route that combines the existing PATCH with
the new cover endpoints. Cover PUT cleans up the old blob when the
extension changes, swallowing StorageError::NotFound so a manually-gone
file doesn't surface as a 404 to the client. Edit link on the manga
detail page is gated on session.user, matching the auth posture of the
underlying handlers.

Also pins the local-dev port story via loadEnv() in vite.config.ts so
VITE_PORT / BACKEND_URL from a (gitignored) .env keep the dev URL
stable across runs.

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

frontend/e2e/manga-edit.spec.ts

@@ -0,0 +1,147 @@
+import { test, expect, type Page } from '@playwright/test';
+
+const userFixture = {
+    id: 'u1',
+    username: 'alice',
+    created_at: '2026-01-01T00:00:00Z'
+};
+
+const baseManga = {
+    id: 'm1',
+    title: 'Berserk',
+    status: 'ongoing',
+    alt_titles: ['Old Alt'],
+    description: 'Original description',
+    cover_image_path: null,
+    created_at: '2026-01-01T00:00:00Z',
+    updated_at: '2026-01-01T00:00:00Z',
+    authors: [{ id: 'a1', name: 'Kentaro Miura' }],
+    genres: [],
+    tags: []
+};
+
+async function stubAuthenticatedAndGenres(page: Page) {
+    await page.route('**/api/v1/auth/me', (route) =>
+        route.fulfill({
+            status: 200,
+            contentType: 'application/json',
+            body: JSON.stringify({ user: userFixture })
+        })
+    );
+    await page.route('**/api/v1/genres', (route) =>
+        route.fulfill({
+            status: 200,
+            contentType: 'application/json',
+            body: JSON.stringify([
+                { id: 'g-action', name: 'Action' },
+                { id: 'g-fantasy', name: 'Fantasy' }
+            ])
+        })
+    );
+}
+
+test('anonymous user sees sign-in prompt on /manga/[id]/edit', async ({ page }) => {
+    await page.route('**/api/v1/auth/me', (route) =>
+        route.fulfill({
+            status: 401,
+            contentType: 'application/json',
+            body: JSON.stringify({
+                error: { code: 'unauthenticated', message: 'unauthenticated' }
+            })
+        })
+    );
+    await page.route('**/api/v1/genres', (route) =>
+        route.fulfill({ status: 200, contentType: 'application/json', body: '[]' })
+    );
+    await page.route('**/api/v1/mangas/m1', (route) =>
+        route.fulfill({
+            status: 200,
+            contentType: 'application/json',
+            body: JSON.stringify(baseManga)
+        })
+    );
+
+    await page.goto('/manga/m1/edit');
+    await expect(page.getByTestId('edit-signin')).toBeVisible();
+});
+
+test('/manga/[id]/edit PATCHes the changed metadata and lands on the manga page', async ({
+    page
+}) => {
+    await stubAuthenticatedAndGenres(page);
+
+    let patchBody: Record<string, unknown> | null = null;
+    let mangaAfter = { ...baseManga };
+    await page.route('**/api/v1/mangas/m1', async (route) => {
+        const method = route.request().method();
+        if (method === 'GET') {
+            await route.fulfill({
+                status: 200,
+                contentType: 'application/json',
+                body: JSON.stringify(mangaAfter)
+            });
+        } else if (method === 'PATCH') {
+            patchBody = JSON.parse(route.request().postData() ?? '{}');
+            mangaAfter = {
+                ...mangaAfter,
+                title: (patchBody.title as string) ?? mangaAfter.title,
+                description:
+                    'description' in (patchBody as Record<string, unknown>)
+                        ? ((patchBody.description as string | null) ?? null)
+                        : mangaAfter.description
+            };
+            await route.fulfill({
+                status: 200,
+                contentType: 'application/json',
+                body: JSON.stringify(mangaAfter)
+            });
+        } else {
+            await route.fallback();
+        }
+    });
+    await page.route('**/api/v1/mangas/m1/chapters*', (route) =>
+        route.fulfill({
+            status: 200,
+            contentType: 'application/json',
+            body: JSON.stringify({
+                items: [],
+                page: { limit: 50, offset: 0, total: 0 }
+            })
+        })
+    );
+    await page.route('**/api/v1/me/bookmarks*', (route) =>
+        route.fulfill({
+            status: 200,
+            contentType: 'application/json',
+            body: JSON.stringify({
+                items: [],
+                page: { limit: 50, offset: 0, total: 0 }
+            })
+        })
+    );
+    await page.route('**/api/v1/me/read-progress/m1', (route) =>
+        route.fulfill({
+            status: 404,
+            contentType: 'application/json',
+            body: JSON.stringify({
+                error: { code: 'not_found', message: 'no progress' }
+            })
+        })
+    );
+
+    await page.goto('/manga/m1');
+    // Edit link is gated on session.user — it should be visible to the
+    // stubbed authenticated user.
+    await page.getByTestId('edit-manga-link').click();
+    await expect(page).toHaveURL(/\/manga\/m1\/edit$/);
+
+    const titleInput = page.getByTestId('manga-title');
+    await expect(titleInput).toHaveValue('Berserk');
+    await titleInput.fill('Berserk (Deluxe)');
+    await page.getByTestId('manga-edit-submit').click();
+
+    await expect(page).toHaveURL(/\/manga\/m1$/);
+    await expect(page.getByTestId('manga-title')).toHaveText('Berserk (Deluxe)');
+    expect(patchBody).not.toBeNull();
+    expect((patchBody as Record<string, unknown>).title).toBe('Berserk (Deluxe)');
+});