fix: HA light target — brightness source, transition=0, dashboard type label

- Add brightness_value_source_id to HALightOutputTarget model, to_dict,
  from_dict, update_fields, register_with_manager, API response
- Wire value stream in HALightTargetProcessor: acquire/release on
  start/stop, multiply brightness in _update_lights loop
- Fix transition=0 not saving (parseFloat("0") || 0.5 was falsy)
- Fix dashboard showing "Key Colors" for HA targets — now "Home Assistant"
- Fix dashboard FPS showing 0/2 — HA targets show target/target
- Add CSS source subtitle to HA target dashboard cards

server/pyproject.toml

@@ -47,6 +47,7 @@ dependencies = [
     "openrgb-python>=0.2.15",
     "opencv-python-headless>=4.8.0",
     "websockets>=13.0",
+    "just-playback>=0.1.7",
 ]
 
 [project.optional-dependencies]