feat: Presence Layer API implementation

Matrix Gateway:
- GET /internal/matrix/presence/{matrix_user_id} - get single user presence
- GET /internal/matrix/presence/bulk - get multiple users presence

City Service:
- GET /api/v1/agents/{agent_id}/presence - get agent presence via gateway
- get_matrix_presence_for_user() helper function

Task doc: TASK_PHASE_PRESENCE_LAYER_v1.md

services/city-service/routes_city.py

@@ -1736,6 +1736,61 @@ async def get_agents_presence():
         raise HTTPException(status_code=500, detail="Failed to get agents presence")
 
 
+@api_router.get("/agents/{agent_id}/presence")
+async def get_single_agent_presence(agent_id: str):
+    """
+    Отримати presence статус одного агента.
+    Використовує Matrix Gateway для отримання реального статусу.
+    """
+    try:
+        # Get agent from DB
+        agent = await repo_city.get_agent_by_id(agent_id)
+        if not agent:
+            raise HTTPException(status_code=404, detail=f"Agent not found: {agent_id}")
+        
+        # Get Matrix user ID for agent (or generate it)
+        # Pattern: @agent_{slug}:daarion.space
+        agent_slug = agent.get("public_slug") or agent_id.replace("ag_", "").replace("-", "_")
+        matrix_user_id = f"@agent_{agent_slug}:daarion.space"
+        
+        # Get presence from Matrix Gateway
+        presence_data = await get_matrix_presence_for_user(matrix_user_id)
+        
+        return {
+            "agent_id": agent_id,
+            "display_name": agent.get("display_name"),
+            "matrix_user_id": matrix_user_id,
+            "presence": presence_data.get("presence", "offline"),
+            "last_active_ago_ms": presence_data.get("last_active_ago_ms"),
+            "status_msg": presence_data.get("status_msg")
+        }
+    except HTTPException:
+        raise
+    except Exception as e:
+        logger.error(f"Failed to get agent presence for {agent_id}: {e}")
+        raise HTTPException(status_code=500, detail="Failed to get agent presence")
+
+
+async def get_matrix_presence_for_user(matrix_user_id: str) -> dict:
+    """
+    Get Matrix presence for a single user via Matrix Gateway.
+    """
+    try:
+        gateway_url = os.getenv("MATRIX_GATEWAY_URL", "http://daarion-matrix-gateway:7025")
+        async with httpx.AsyncClient(timeout=5.0) as client:
+            # URL encode the matrix user ID
+            encoded_mxid = matrix_user_id.replace("@", "%40").replace(":", "%3A")
+            response = await client.get(f"{gateway_url}/internal/matrix/presence/{encoded_mxid}")
+            if response.status_code == 200:
+                return response.json()
+            else:
+                logger.warning(f"Matrix gateway presence returned {response.status_code}")
+                return {"presence": "offline"}
+    except Exception as e:
+        logger.warning(f"Failed to get Matrix presence for {matrix_user_id}: {e}")
+        return {"presence": "offline"}
+
+
 async def get_matrix_presence_status():
     """
     Get Matrix presence from matrix-presence-aggregator.