feat: switch LLM to OpenWebUI with live model selection

- Point the agent at OpenWebUI's OpenAI-compatible API (LLM_BASE_URL,
  LLM_API_KEY, LLM_MODEL) with GEMMA_* env fallbacks
- Add list_available_models() fetching {base_url}/models, filtering
  non-chat ids (embedding/reranker)
- Rename GemmaLLM -> HopeLLM with update_options(model=...) for runtime
  model switching (mutates _opts.model) and instance-based compaction
- Data channel: agent publishes {type: models} after connect and on
  get_models; set_model switches live and acks model_changed
- Web UI: Brain section in the settings sheet with a model picker that
  persists the choice in localStorage
- Update tests, CI workflow env, and docs for the new endpoint

docker-compose.yml

@@ -10,9 +10,9 @@ services:
       AZURE_SPEECH_KEY: "${AZURE_SPEECH_KEY:?Set AZURE_SPEECH_KEY in .env}"
       AZURE_SPEECH_REGION: "${AZURE_SPEECH_REGION:-eastus}"
       AZURE_TTS_VOICE: "${AZURE_TTS_VOICE:-en-US-Ava:DragonHDOmniLatestNeural}"
-      GEMMA_BASE_URL: "${GEMMA_BASE_URL:-http://192.168.86.2:8023/v1}"
-      GEMMA_MODEL: "${GEMMA_MODEL:-gemma-4-e4b}"
-      GEMMA_API_KEY: "${GEMMA_API_KEY:-not-needed}"
+      LLM_BASE_URL: "${LLM_BASE_URL:-http://192.168.86.2:3005/api}"
+      LLM_MODEL: "${LLM_MODEL:-gemma-4-e4b}"
+      LLM_API_KEY: "${LLM_API_KEY:-not-needed}"
       WEB_MCP_ENABLED: "${WEB_MCP_ENABLED:-true}"
       FIRECRAWL_BASE: "${FIRECRAWL_BASE:-http://192.168.86.2:3002}"
       WEB_PORT: "${WEB_PORT:-9178}"