feat(web): add network-only PWA installability (#6190)

* feat(web): add network-only PWA installability

Serve the manifest, registration script, network-only service worker, and icons under the runtime web base path so panels remain installable at arbitrary configured URLs.

This does not add offline caching or change panel, API, database, or Xray behavior.

* chore(docs): remove development planning notes

Keep the pull request focused on the PWA implementation, tests, and user-facing verification documentation.

* feat(web): adopt the 3X logo PWA icon set from #1865

Replace the two placeholder SVG icons with the six-size PNG set
(16/24/32/64/192/512) contributed by @Incognito-Coder in PR #1865.
The PNGs have transparent rounded corners, so the manifest entries
drop the maskable purpose claim and rely on the default any.

---------

Co-authored-by: korsun009 <277924786+korsun009@users.noreply.github.com>
Co-authored-by: Sanaei <ho3ein.sanaei@gmail.com>

frontend/public/manifest.webmanifest

@@ -0,0 +1,41 @@
+{
+  "name": "3x-ui",
+  "short_name": "3x-ui",
+  "start_url": "./",
+  "scope": "./",
+  "display": "standalone",
+  "background_color": "#0f172a",
+  "theme_color": "#1677ff",
+  "icons": [
+    {
+      "src": "icons/3x-ui-16.png",
+      "sizes": "16x16",
+      "type": "image/png"
+    },
+    {
+      "src": "icons/3x-ui-24.png",
+      "sizes": "24x24",
+      "type": "image/png"
+    },
+    {
+      "src": "icons/3x-ui-32.png",
+      "sizes": "32x32",
+      "type": "image/png"
+    },
+    {
+      "src": "icons/3x-ui-64.png",
+      "sizes": "64x64",
+      "type": "image/png"
+    },
+    {
+      "src": "icons/3x-ui-192.png",
+      "sizes": "192x192",
+      "type": "image/png"
+    },
+    {
+      "src": "icons/3x-ui-512.png",
+      "sizes": "512x512",
+      "type": "image/png"
+    }
+  ]
+}

frontend/public/pwa-register.js

@@ -0,0 +1,14 @@
+(() => {
+  if (!('serviceWorker' in navigator)) return;
+
+  const script = document.currentScript;
+  if (!(script instanceof HTMLScriptElement)) return;
+
+  const scriptUrl = new URL(script.src, window.location.href);
+  const baseUrl = new URL('./', scriptUrl);
+  const workerUrl = new URL('service-worker.js', baseUrl);
+
+  navigator.serviceWorker.register(workerUrl.pathname, {
+    scope: baseUrl.pathname,
+  }).catch(() => {});
+})();

frontend/public/service-worker.js

@@ -0,0 +1,9 @@
+self.addEventListener('install', (event) => {
+  event.waitUntil(self.skipWaiting());
+});
+
+self.addEventListener('activate', (event) => {
+  event.waitUntil(self.clients.claim());
+});
+
+self.addEventListener('fetch', () => {});