feat: replace custom memory MCP with Cognee remote server

- Remove memory_mcp.py (stdio markdown-file memory)
- Add Cognee MCP as remote Streamable HTTP toolset at 192.168.86.2:8003/mcp
- Filter to only remember/recall/forget tools via allowed_tools
- Update system prompt: Memory section moved to top priority with
  explicit 'call recall FIRST' instructions and examples
- Add COGNEE_MCP_URL env var to docker-compose
- Remove /memory volume mount (no longer needed)
- Rewrite memory tests to use Cognee HTTP client fixture
- 28/28 tests passing

tests/conftest.py

@@ -19,6 +19,7 @@ WEB_BASE_URL = os.environ.get("VOICE_WEB_URL", "https://localhost:8090")
 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")
+COGNEE_MCP_URL = os.environ.get("COGNEE_MCP_URL", "http://192.168.86.2:8003/mcp")
 
 # Path to the agent's venv python inside the container (has mcp, livekit.agents)
 CONTAINER_PYTHON = "/opt/voice-agent/.venv/bin/python"
@@ -134,3 +135,42 @@ asyncio.run(main())
         return data["text"], data["isError"]
 
     return _call
+
+
+@pytest.fixture(scope="session")
+def cognee_client():
+    """Factory that calls tools on the remote Cognee MCP server (Streamable HTTP).
+
+    Returns (result_text, is_error). Uses the mcp client library from the
+    agent venv inside the container.
+    """
+
+    def _call(tool_name: str, args: dict | None = None) -> tuple[str, bool]:
+        code = f"""
+import asyncio, json
+from mcp import ClientSession
+from mcp.client.streamable_http import streamablehttp_client
+
+async def main():
+    async with streamablehttp_client({COGNEE_MCP_URL!r}) as (read, write, _):
+        async with ClientSession(read, write) as session:
+            await session.initialize()
+            result = await session.call_tool({tool_name!r}, {json.dumps(args or {})})
+            text = ""
+            for block in result.content:
+                if getattr(block, "type", None) == "text":
+                    text += block.text
+            print(json.dumps({{"text": text, "isError": bool(result.isError)}}))
+
+asyncio.run(main())
+"""
+        proc = docker_exec_python(code, timeout=120, check=False)
+        if proc.returncode != 0:
+            raise AssertionError(
+                f"Cognee MCP call {tool_name} failed (rc={proc.returncode}): "
+                f"stderr={proc.stderr[-800:]}"
+            )
+        data = json.loads(proc.stdout.strip().splitlines()[-1])
+        return data["text"], data["isError"]
+
+    return _call