fix: PWA install prompt - add PNG icons and fix apple-touch-icon

Browsers require PNG icons (192x192, 512x512) in the manifest to show
the install prompt. SVG-only manifests are not sufficient. Also adds the
180x180 apple-touch-icon PNG for iOS home screen, bumps SW cache to v3,
and adds scope to the manifest.

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

static/manifest.json

@@ -3,10 +3,21 @@
   "short_name": "INTERCEPT",
   "description": "Unified SIGINT platform for software-defined radio analysis",
   "start_url": "/",
+  "scope": "/",
   "display": "standalone",
   "background_color": "#0b1118",
   "theme_color": "#0b1118",
   "icons": [
+    {
+      "src": "/static/icons/icon-192.png",
+      "sizes": "192x192",
+      "type": "image/png"
+    },
+    {
+      "src": "/static/icons/icon-512.png",
+      "sizes": "512x512",
+      "type": "image/png"
+    },
     {
       "src": "/static/icons/icon.svg",
       "sizes": "any",

static/sw.js

@@ -1,5 +1,5 @@
 /* INTERCEPT Service Worker — cache-first static, network-only for API/SSE/WS */
-const CACHE_NAME = 'intercept-v2';
+const CACHE_NAME = 'intercept-v3';
 
 const NETWORK_ONLY_PREFIXES = [
     '/stream', '/ws/', '/api/', '/gps/', '/wifi/', '/bluetooth/',

templates/index.html

@@ -10,7 +10,7 @@
     <meta name="theme-color" content="#0b1118">
     <meta name="mobile-web-app-capable" content="yes">
     <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent">
-    <link rel="apple-touch-icon" href="/static/icons/icon.svg">
+    <link rel="apple-touch-icon" href="/static/icons/apple-touch-icon.png">
     <!-- Disclaimer gate - must accept before seeing welcome page -->
     <script>
         // Check BEFORE page renders - if disclaimer not accepted, hide welcome page