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/vite.config.ts

@@ -1,20 +1,26 @@
 import { sveltekit } from '@sveltejs/kit/vite';
-import { defineConfig } from 'vite';
+import { defineConfig, loadEnv } from 'vite';
 
-export default defineConfig({
-    plugins: [sveltekit()],
-    server: {
-        port: 5173,
-        proxy: {
-            '/api': {
-                target: process.env.BACKEND_URL ?? 'http://localhost:8080',
-                changeOrigin: true
+export default defineConfig(({ mode }) => {
+    // Pull in .env so VITE_PORT / BACKEND_URL pin the dev URL across runs.
+    // Empty prefix loads every key, not just VITE_*.
+    const env = { ...process.env, ...loadEnv(mode, process.cwd(), '') };
+    return {
+        plugins: [sveltekit()],
+        server: {
+            port: Number(env.VITE_PORT ?? 5173),
+            strictPort: env.VITE_PORT != null,
+            proxy: {
+                '/api': {
+                    target: env.BACKEND_URL ?? 'http://localhost:8080',
+                    changeOrigin: true
+                }
             }
+        },
+        test: {
+            environment: 'jsdom',
+            include: ['src/**/*.test.ts'],
+            globals: false
         }
-    },
-    test: {
-        environment: 'jsdom',
-        include: ['src/**/*.test.ts'],
-        globals: false
-    }
+    };
 });