Add toast notification for wrapped long URLs in terminal

PTY hard-wraps long URLs (e.g. OAuth) with \r\n at column width, breaking
xterm.js link detection. This adds a UrlDetector that reassembles wrapped
URLs from the output stream and shows a non-intrusive floating toast with
an "Open" button. Auto-dismisses after 30s, no terminal layout impact.

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

app/src/index.css

@@ -46,3 +46,10 @@ body {
 ::-webkit-scrollbar-thumb:hover {
   background: var(--border-color);
 }
+
+/* Toast slide-down animation */
+@keyframes slide-down {
+  from { opacity: 0; transform: translate(-50%, -8px); }
+  to   { opacity: 1; transform: translate(-50%, 0); }
+}
+.animate-slide-down { animation: slide-down 0.2s ease-out; }