feat: add MCP tool integration

backend/models.py

@@ -15,6 +15,18 @@ from pydantic import BaseModel, Field
 RuntimeMode = Literal["pipeline", "realtime"]
 
 
+class RuntimeMcpServer(BaseModel):
+    """Resolved MCP connection containing secrets for one runtime session."""
+
+    id: str
+    name: str = ""
+    transport: str = "streamable_http"
+    url: str
+    timeout_seconds: int = 30
+    headers: dict[str, str] = Field(default_factory=dict)
+    secret_headers: dict[str, str] = Field(default_factory=dict)
+
+
 class RuntimeTool(BaseModel):
     """Tool data resolved from an assistant binding for one runtime session."""
 
@@ -25,6 +37,7 @@ class RuntimeTool(BaseModel):
     description: str = ""
     definition: dict = Field(default_factory=dict)
     secrets: dict = Field(default_factory=dict)
+    mcp_server: RuntimeMcpServer | None = None
 
 
 class RuntimeModelResource(BaseModel):