feat(monitor): WS client live stream + apply snapshot/delta to UI

Hand-rolled minimal RFC6455 WebSocket client (~330 LOC) tailored to the
Monitor tab's needs. Single endpoint, text frames, masked client→server,
exponential reconnect backoff (0.5s → 8s cap), thread-safe in/out queues.
TLS is intentionally out of scope (localhost-only). Sec-WebSocket-Accept
verification is skipped — the server is controlled, 101 status is enough.

Files:
- ws_client.{h,cpp}: WsClient with start(host,port,path), drain(), send_text(),
  is_connected(), last_event_ts(). Worker thread does connect + handshake +
  read_loop + reconnect.
- CMakeLists.txt: pulls ws_client.cpp into the dashboard target. ws2_32 was
  already linked for http_client.cpp.
- main.cpp: parses host:port from --api URL, spawns a global WsClient, and
  drains its queue once per render frame via poll_ws(). apply_ws_message()
  routes JSON to g_data.claude:
    snapshot → replace KPIs + recent_executions
    delta    → append rows, increment total_calls / total_errors
  monitor_set_ws_state() forwards connection state + last_event_ts to the
  Monitor toolbar LED.

End-to-end smoke test passed against sqlite_api on localhost:8484:
- Snapshot received with KPIs + 100 recent rows.
- After INSERT INTO calls, delta arrives within ~250ms (server ticker).
- Errors (success=0) propagate correctly and bump the Errors KPI.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CMakeLists.txt

@@ -19,6 +19,7 @@ add_imgui_app(registry_dashboard
     data.cpp
     data_http.cpp
     http_client.cpp
+    ws_client.cpp
     views.cpp
     ${CMAKE_SOURCE_DIR}/functions/viz/kpi_card.cpp
     ${CMAKE_SOURCE_DIR}/functions/viz/bar_chart.cpp