Add NextSnap PWA with photo gallery viewer and continuous capture

Offline-first photo capture app for Nextcloud with:
- Camera capture with continuous mode (auto-reopens after each photo)
- File browser with fullscreen image gallery, swipe navigation, and rename
- Upload queue with background sync engine
- Admin panel for Nextcloud user management
- Service worker for offline-first caching (v13)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/static/manifest.json

@@ -0,0 +1,27 @@
+{
+    name: NextSnap,
+    short_name: NextSnap,
+    description: Offline-first photo capture for Nextcloud,
+    start_url: /,
+    display: standalone,
+    orientation: portrait,
+    background_color: #1a1a2e,
+    theme_color: #16213e,
+    icons: [
+        {
+            src: /static/icons/icon-192.png,
+            sizes: 192x192,
+            type: image/png,
+            purpose: any maskable
+        },
+        {
+            src: /static/icons/icon-512.png,
+            sizes: 512x512,
+            type: image/png,
+            purpose: any maskable
+        }
+    ],
+    categories: [productivity, photo],
+    scope: /,
+    prefer_related_applications: false
+}