feat: add iOS Safari install guide and improve PWA UX with neutral theme

- Add iOS Safari install prompt with step-by-step modal guide
- Fix Telegram environment detection (check initData, not just SDK presence)
- Fix install prompt re-entrancy issue (clear deferredPrompt immediately)
- Extract icon components to separate file (web/src/components/icons.tsx)
- Rename "Happy App" to "Hapi" throughout the UI and manifests
- Change button/icon colors from blue (--app-button) to neutral theme (--app-fg/--app-bg)
- Add install dismiss state to prevent repeated prompts
- Improve iOS Safari detection with robust user agent parsing

web/src/index.css

@@ -145,3 +145,19 @@ html[data-theme="dark"] .shiki span {
   animation: rainbow-wave 2s linear infinite, sparkle-wave 2s ease-in-out infinite;
   font-weight: 600;
 }
+
+/* PWA install prompt animation */
+@keyframes slide-up {
+  from {
+    transform: translateY(100%);
+    opacity: 0;
+  }
+  to {
+    transform: translateY(0);
+    opacity: 1;
+  }
+}
+
+.animate-slide-up {
+  animation: slide-up 0.3s ease-out;
+}