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

scripts/ralph/ralph_once.sh

@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+# Human-in-the-loop Ralph: runs exactly one iteration
+# Use this to observe behavior before going fully autonomous
+
+set -euo pipefail
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+
+export MAX_ITERATIONS=1
+exec "$SCRIPT_DIR/ralph.sh" "$@"