Allow referencing other apps (#692)

- [x] Update chat_stream_handlers
- [x] Update token handlers
- [x] Update HomeChatInput
- [x] update lexical chat input: do not allow referencing same app
(current app, or other already selected apps)
- [x] I don't think smart context will work on this...
- [x] Enter doesn't clear...

src/shared/parse_mention_apps.ts

@@ -0,0 +1,13 @@
+// Helper function to parse app mentions from prompt
+export function parseAppMentions(prompt: string): string[] {
+  // Match @app:AppName patterns in the prompt (supports letters, digits, underscores, and hyphens, but NOT spaces)
+  const mentionRegex = /@app:([a-zA-Z0-9_-]+)/g;
+  const mentions: string[] = [];
+  let match;
+
+  while ((match = mentionRegex.exec(prompt)) !== null) {
+    mentions.push(match[1]);
+  }
+
+  return mentions;
+}