Add Home Assistant WebSocket client module

- New ha_client.rs: background-thread WebSocket client using tungstenite
  with rustls TLS. Handles auth, state subscription, service calls, and
  recorder/statistics history fetch for climate graphs. Auto-reconnects
  on disconnect with 5s delay.
- HaState added to State struct: tracks connection status, entity states,
  and temperature history per entity.
- main.rs loads ha-home/config.json at startup, extracts all referenced
  entity IDs, and creates the HaService. ha_tick() drains responses into
  state each frame, matching the weather_tick pattern.
- tungstenite 0.24 added to Cargo.toml with handshake + rustls features.

All 84 existing tests pass.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Cargo.toml

@@ -26,6 +26,7 @@ sdl2 = { version = "0.38", features = ["use-pkgconfig"] }
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 time = { version = "0.3", features = ["local-offset", "formatting", "parsing"] }
+tungstenite = { version = "0.24", default-features = false, features = ["handshake", "rustls-tls-native-roots"] }
 ureq = { version = "3.4", default-features = false, features = ["rustls"] }
 
 [profile.release]