Add dynamic variable support to Assistant model and related components

- Introduce dynamic variable definitions in AssistantConfig and Assistant models, allowing for flexible prompt customization.
- Implement validation for dynamic variable names and types in the schema.
- Update backend services and routes to handle dynamic variables in assistant configurations and runtime processing.
- Enhance frontend components to support dynamic variable definitions, including a new editor for managing variables.
- Add tests to ensure proper functionality and validation of dynamic variables in various scenarios.

backend/services/pipecat/stepfun_realtime.py

@@ -289,6 +289,12 @@ class StepFunRealtimeService(AIService):
             wait_until_ready=False,
         )
 
+    async def update_instructions(self, instructions: str) -> None:
+        """Refresh model instructions without rebuilding the realtime session."""
+        self._instructions = instructions
+        if self._session_ready.is_set():
+            await self._send_session_update()
+
     async def _send_event(
         self, payload: dict[str, Any], *, wait_until_ready: bool = True
     ) -> None: