feat: add WebVTT context generation to chat WebSocket endpoint

- Import topics_to_webvtt_named and recordings controller
- Add _get_is_multitrack helper function
- Generate WebVTT context on WebSocket connection
- Add get_context message type to retrieve WebVTT
- Maintain backward compatibility with echo for other messages
- Add test fixture and test for WebVTT context generation

Implements task fn-1.2: WebVTT context generation for transcript chat

.flow/specs/fn-1.2.md

@@ -0,0 +1,43 @@
+# Task 2: WebVTT Context Generation
+
+**File:** `server/reflector/views/transcripts_chat.py` (modify)
+**Lines:** ~15
+**Dependencies:** Task 1
+
+## Objective
+Generate WebVTT transcript context on connection.
+
+## Implementation
+```python
+from reflector.utils.transcript_formats import topics_to_webvtt_named
+from reflector.views.transcripts import _get_is_multitrack
+
+# Add after websocket.accept():
+# Get WebVTT context
+is_multitrack = await _get_is_multitrack(transcript)
+webvtt = topics_to_webvtt_named(
+    transcript.topics,
+    transcript.participants,
+    is_multitrack
+)
+
+# Truncate if needed
+webvtt_truncated = webvtt[:15000] if len(webvtt) > 15000 else webvtt
+
+# Send to client for verification
+await websocket.send_json({
+    "type": "context",
+    "webvtt": webvtt_truncated,
+    "truncated": len(webvtt) > 15000
+})
+```
+
+## Validation
+- [ ] WebVTT generated on connection
+- [ ] Truncated to 15k chars if needed
+- [ ] Client receives context message
+- [ ] Format matches WebVTT spec (timestamps, speaker names)
+
+## Notes
+- Log if truncation occurs
+- Keep echo functionality for testing