fix(pwa): resolve manifest warnings for cleaner PWA install experience

- Fix icon purpose from "any maskable" to "any" to avoid incorrect
  padding on some platforms
- Add explicit id field matching start_url to stabilise the App ID
- Add display_override with window-controls-overlay for native title bar
- Register web+holesail:// protocol handler so installed app can be
  launched directly from custom protocol links

extension/dashboard/manifest.webmanifest

@@ -1,11 +1,19 @@
 {
+  "id": "/dashboard/dashboard.html",
   "name": "Holesail Browser",
   "short_name": "Holesail",
   "description": "P2P Holesail tunnels in the browser",
   "start_url": "dashboard.html",
   "display": "standalone",
+  "display_override": ["window-controls-overlay", "standalone"],
   "background_color": "#0f1117",
   "theme_color": "#0f1117",
+  "protocol_handlers": [
+    {
+      "protocol": "web+holesail",
+      "url": "dashboard.html?lookup=%s"
+    }
+  ],
   "screenshots": [
     {
       "src": "screenshots/wide.png",
@@ -23,9 +31,9 @@
     }
   ],
   "icons": [
-    { "src": "../icons/48.png",  "sizes": "48x48",   "type": "image/png" },
-    { "src": "../icons/128.png", "sizes": "128x128", "type": "image/png" },
-    { "src": "../icons/192.png", "sizes": "192x192", "type": "image/png" },
-    { "src": "../icons/512.png", "sizes": "512x512", "type": "image/png", "purpose": "any maskable" }
+    { "src": "../icons/48.png",  "sizes": "48x48",   "type": "image/png", "purpose": "any" },
+    { "src": "../icons/128.png", "sizes": "128x128", "type": "image/png", "purpose": "any" },
+    { "src": "../icons/192.png", "sizes": "192x192", "type": "image/png", "purpose": "any" },
+    { "src": "../icons/512.png", "sizes": "512x512", "type": "image/png", "purpose": "any" }
   ]
 }