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/LoginForm.tsx

@@ -175,14 +175,6 @@ export function LoginForm() {
             {isRegister ? "[BACK TO LOGIN]" : "[CREATE ACCOUNT]"}
           </button>
         </div>
-        {!isRegister && (
-          <p className="text-gb-fg-f text-xs mt-4 text-center">
-            Use Link component:{" "}
-            <Link to="/" className="text-gb-blue hover:text-gb-aqua">
-              [HOME]
-            </Link>
-          </p>
-        )}
       </div>
     </div>
   );