feat(discord): add listen_to_bots config and fix model IDs across codebase (#280)

* fix(config): apply env overrides at runtime and fix Docker compose defaults

- Call apply_env_overrides() after Config::load_or_init() in main.rs so
  environment variables (API_KEY, PROVIDER, ZEROCLAW_GATEWAY_PORT, etc.)
  are actually applied at runtime, not just in tests
- Add ZEROCLAW_ALLOW_PUBLIC_BIND env var support for gateway bind policy
- Fix docker-compose.yml: correct volume path (/zeroclaw-data not /data),
  add ZEROCLAW_ALLOW_PUBLIC_BIND=true for container networking, make host
  port configurable via HOST_PORT env var
- Add docker-compose.override.yml to .gitignore for local dev overrides

* feat(discord): add listen_to_bots config and fix model IDs across codebase

Add listen_to_bots field to DiscordConfig so bot messages are processed
when explicitly enabled (defaults to false for backward compat). Remove
ZEROCLAW_MODEL from Dockerfile release stage so config.toml is the
source of truth for model selection. Fix all hardcoded model IDs from
the dated anthropic/claude-sonnet-4-20250514 to the valid OpenRouter
identifier anthropic/claude-sonnet-4.

src/gateway/mod.rs

@@ -198,7 +198,7 @@ pub async fn run_gateway(host: &str, port: u16, config: Config) -> Result<()> {
     let model = config
         .default_model
         .clone()
-        .unwrap_or_else(|| "anthropic/claude-sonnet-4-20250514".into());
+        .unwrap_or_else(|| "anthropic/claude-sonnet-4".into());
     let temperature = config.default_temperature;
     let mem: Arc<dyn Memory> = Arc::from(memory::create_memory(
         &config.memory,