feat: PWA overhaul

- Remove debug artifact from login page ('Use Link component: HOME')
- Full icon set: 48/72/96/128/144/152/192/384/512 + maskable variants
- Proper manifest: display_override, shortcuts, categories, scope
- Better service worker: offline fallback page, pre-caching, stale-while-revalidate
- Custom install banner (Android beforeinstallprompt + iOS instructions)
- Connection status indicator (online/offline toast)
- Updated index.html with proper favicon sizes and meta tags

web/src/components/ConnectionStatus.tsx

@@ -0,0 +1,40 @@
+import { useState, useEffect } from "react";
+
+export function ConnectionStatus() {
+  const [online, setOnline] = useState(navigator.onLine);
+  const [visible, setVisible] = useState(!navigator.onLine);
+
+  useEffect(() => {
+    const handleOnline = () => {
+      setOnline(true);
+      // Show "back online" briefly then hide
+      setVisible(true);
+      setTimeout(() => setVisible(false), 3000);
+    };
+    const handleOffline = () => {
+      setOnline(false);
+      setVisible(true);
+    };
+
+    window.addEventListener("online", handleOnline);
+    window.addEventListener("offline", handleOffline);
+    return () => {
+      window.removeEventListener("online", handleOnline);
+      window.removeEventListener("offline", handleOffline);
+    };
+  }, []);
+
+  if (!visible) return null;
+
+  return (
+    <div
+      className={`fixed top-0 left-0 right-0 z-[100] text-center py-1 text-xs font-mono transition-all duration-300 ${
+        online
+          ? "bg-gb-green/20 text-gb-green border-b border-gb-green/30"
+          : "bg-gb-red/20 text-gb-red border-b border-gb-red/30"
+      }`}
+    >
+      {online ? "● CONNECTION RESTORED" : "○ YOU ARE OFFLINE — messages will send when reconnected"}
+    </div>
+  );
+}