Live updates over WebSocket + clickable links

- Connect to the server's /ws multiplexed socket (chat/notifications/board) for
  the whole authenticated session. Auth rides the existing cookie jar; no server
  changes needed (the server allows clients that send no Origin header).
- Chat now updates live: ConversationViewModel merges messages pushed over the
  socket for the open conversation (no more leaving/re-entering to see replies).
- Notifications are now real-time in-app (bell updates instantly); when the app is
  backgrounded, incoming alerts and messages raise a system notification via the
  same socket. The 15-min WorkManager poll remains as a catch-up safety net.
- Links are now clickable in chat messages, task comments, and descriptions via a
  new RichText component (handles <a> anchors and bare http/www URLs).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/src/main/java/com/anypreta/bountyboard/MainActivity.kt

@@ -57,4 +57,14 @@ class MainActivity : ComponentActivity() {
         val container = (application as BountyBoardApp).container
         intent.getStringExtra(PushNotifier.EXTRA_ROUTE)?.let { container.setDeepLink(it) }
     }
+
+    override fun onStart() {
+        super.onStart()
+        (application as BountyBoardApp).container.appForeground = true
+    }
+
+    override fun onStop() {
+        super.onStop()
+        (application as BountyBoardApp).container.appForeground = false
+    }
 }