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.

Dockerfile

@@ -94,9 +94,9 @@ COPY --from=permissions /zeroclaw-data /zeroclaw-data
 # Environment setup
 ENV ZEROCLAW_WORKSPACE=/zeroclaw-data/workspace
 ENV HOME=/zeroclaw-data
-# Defaults for prod (OpenRouter)
+# Default provider (model is set in config.toml, not here,
+# so config file edits are not silently overridden)
 ENV PROVIDER="openrouter"
-ENV ZEROCLAW_MODEL="anthropic/claude-sonnet-4-20250514"
 ENV ZEROCLAW_GATEWAY_PORT=3000
 
 # API_KEY must be provided at runtime!