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

tests/conftest.py

@@ -3,7 +3,7 @@
 Tests run on the HOST machine against the live "voice" container:
 - HTTPS web UI  -> https://localhost:9178 (self-signed cert, verify=False)
 - Token server  -> http://127.0.0.1:8091 (host network mode)
-- LLM API       -> GEMMA_BASE_URL (default http://192.168.86.2:8023/v1)
+- LLM API       -> LLM_BASE_URL (default http://192.168.86.2:3005/api)
 - In-container  -> docker exec voice ...
 """
 
@@ -18,8 +18,21 @@ import pytest
 CONTAINER = "voice"
 WEB_BASE_URL = os.environ.get("VOICE_WEB_URL", "https://localhost:9178")
 TOKEN_URL = os.environ.get("VOICE_TOKEN_URL", "http://127.0.0.1:8091/token")
-GEMMA_BASE_URL = os.environ.get("GEMMA_BASE_URL", "http://192.168.86.2:8023/v1").rstrip("/")
-GEMMA_MODEL = os.environ.get("GEMMA_MODEL", "gemma-4-e4b")
+LLM_BASE_URL = (
+    os.environ.get("LLM_BASE_URL")
+    or os.environ.get("GEMMA_BASE_URL")
+    or "http://192.168.86.2:3005/api"
+).rstrip("/")
+LLM_MODEL = (
+    os.environ.get("LLM_MODEL")
+    or os.environ.get("GEMMA_MODEL")
+    or "gemma-4-e4b"
+)
+LLM_API_KEY = (
+    os.environ.get("LLM_API_KEY")
+    or os.environ.get("GEMMA_API_KEY")
+    or "not-needed"
+)
 _users = json.loads((Path(__file__).parents[1] / "config" / "users.json").read_text())
 _shane_memory = _users["users"]["shane"]["memory"]
 MEMORY_MCP_URL = os.environ.get("MEMORY_MCP_URL", _shane_memory["url"])
@@ -88,8 +101,11 @@ def token() -> dict:
 
 @pytest.fixture(scope="session")
 def llm_client():
-    """httpx client pointed at the Gemma LLM API (same one Hope uses)."""
-    with httpx.Client(base_url=GEMMA_BASE_URL, timeout=60) as c:
+    """httpx client pointed at the LLM API (same one Hope uses)."""
+    headers = {}
+    if LLM_API_KEY and LLM_API_KEY != "not-needed":
+        headers["Authorization"] = f"Bearer {LLM_API_KEY}"
+    with httpx.Client(base_url=LLM_BASE_URL, headers=headers, timeout=60) as c:
         yield c