feat(phase3): PWA, auto-discovery, bookmarklet, multi-tab sync

- PWA: manifest, service worker (cache-first static, network-first API),
  offline page, install prompt banner
- Auto-discovery: Docker socket + Traefik API scanning, approval UI
- Quick-add bookmarklet: popup-based add page, favicon auto-detect
- Multi-tab sync: BroadcastChannel for theme + data changes
- i18n translations for all new strings (EN/RU)

static/icon.svg

@@ -0,0 +1,7 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512">
+  <rect width="512" height="512" rx="64" fill="#6366f1"/>
+  <rect x="64" y="64" width="160" height="160" rx="16" fill="white"/>
+  <rect x="288" y="64" width="160" height="160" rx="16" fill="white"/>
+  <rect x="64" y="288" width="160" height="160" rx="16" fill="white"/>
+  <rect x="288" y="288" width="160" height="160" rx="16" fill="white"/>
+</svg>

static/manifest.json

@@ -0,0 +1,25 @@
+{
+  "name": "Web App Launcher",
+  "short_name": "Launcher",
+  "start_url": "/",
+  "display": "standalone",
+  "theme_color": "#6366f1",
+  "background_color": "#0a0a0a",
+  "icons": [
+    {
+      "src": "/icon.svg",
+      "sizes": "any",
+      "type": "image/svg+xml"
+    },
+    {
+      "src": "/icon-192.png",
+      "sizes": "192x192",
+      "type": "image/png"
+    },
+    {
+      "src": "/icon-512.png",
+      "sizes": "512x512",
+      "type": "image/png"
+    }
+  ]
+}