feat: Home Assistant integration — WebSocket connection, automation conditions, UI

Add full Home Assistant integration via WebSocket API:
- HARuntime: persistent WebSocket client with auth, auto-reconnect, entity state cache
- HAManager: ref-counted runtime pool (like WeatherManager)
- HomeAssistantCondition: new automation trigger type matching entity states
- REST API: CRUD for HA sources + /test, /entities, /status endpoints
- /api/v1/system/integrations-status: combined MQTT + HA dashboard indicators
- Frontend: HA Sources tab in Streams, condition type in automation editor
- Modal editor with host, token, SSL, entity filters
- websockets>=13.0 dependency added

TODO-css-improvements.md

@@ -111,5 +111,6 @@ Needs deeper design discussion. Likely a new entity type `ColorStripSourceTransi
 
 ## Remaining Open Discussion
 
-1. **`home_assistant` source** — Need to research HAOS communication protocols first
+1. ~~**`home_assistant` source** — Need to research HAOS communication protocols first~~ **DONE** — WebSocket API chosen, connection layer + automation condition + UI implemented
 2. **Transition engine** — Design as `ColorStripSourceTransition` entity: what transition types? (crossfade, wipe, dissolve?) How does a target reference its transition config? How do automations trigger it?
+3. **Home Assistant output targets** — Investigate casting LED colors TO Home Assistant lights (reverse direction). Use HA `light.turn_on` service call with `rgb_color` via WebSocket API. Could enable: ambient lighting on HA-controlled bulbs (Hue, WLED via HA, Zigbee lights), room-by-room color sync, whole-home ambient scenes. Need to research: rate limiting (don't spam HA with 30fps updates), grouping multiple lights, brightness/color_temp mapping, transition parameter support.