feat: wire context engine tools, session lifecycle, and tool dispatch

- Inject engine tool schemas into agent tool surface after compressor init
- Call on_session_start() with session_id, hermes_home, platform, model
- Dispatch engine tool calls (lcm_grep, etc.) before regular tool handler
- 55/55 tests pass

agent/context_engine.py

@@ -118,11 +118,14 @@ class ContextEngine(ABC):
         """
         return []
 
-    def handle_tool_call(self, name: str, args: Dict[str, Any]) -> str:
+    def handle_tool_call(self, name: str, args: Dict[str, Any], **kwargs) -> str:
         """Handle a tool call from the agent.
 
         Only called for tool names returned by get_tool_schemas().
         Must return a JSON string.
+
+        kwargs may include:
+          messages: the current in-memory message list (for live ingestion)
         """
         import json
         return json.dumps({"error": f"Unknown context engine tool: {name}"})