✨(backend) add connection-test API

Currently users have no way to reliably test their connection before
joining a room. To address this, we plan to build a connection-test
page.

The testing requires a dedicated LiveKit token, issued without going
through the room API, which is tied to registered meetings, lobby
rules, and longer-lived access tokens.

Introduce a new viewset for all diagnostics-related features. The
first route issues a token for diagnostics, even for anonymous
users. Each request creates a new dedicated room so users never
share the same LiveKit room during tests. Tokens are short-lived
(default 10 minutes) to limit reuse, and the endpoint is throttled
to prevent abuse.

A Celery worker also schedules a callback that deletes the room
after a certain delay, in every case.

src/backend/core/services/livekit_events.py

@@ -137,6 +137,13 @@ class LiveKitEventsService:
 
         room_name = data.room.name or data.egress_info.room_name
 
+        if self._is_connection_test_room(room_name):
+            logger.info(
+                "Ignoring webhook event for connection test room '%s'.",
+                room_name,
+            )
+            return
+
         if self._filter_regex and not self._filter_regex.search(room_name):
             logger.info("Filtered webhook event for room '%s'", room_name)
             return
@@ -228,6 +235,11 @@ class LiveKitEventsService:
 
         # Silently ignoring EGRESS_ABORTED, EGRESS_FAILED
 
+    @staticmethod
+    def _is_connection_test_room(room_name: str) -> bool:
+        """Return True for ephemeral rooms created by the connection test endpoint."""
+        return room_name.startswith(settings.CONNECTION_TEST_ROOM_PREFIX)
+
     def _handle_room_started(self, data):
         """Handle 'room_started' event."""