fix: move VAD agent creation to RI communication agent

Previously, it was started in main, but it should use values negotiated by the RI communication agent.

ref: N25B-356

src/control_backend/schemas/program_status.py

@@ -0,0 +1,16 @@
+from enum import Enum
+
+PROGRAM_STATUS = b"internal/program_status"
+"""A topic key for the program status."""
+
+
+class ProgramStatus(Enum):
+    """
+    Used in internal communication, to tell agents what the status of the program is.
+
+    For example, the VAD agent only starts listening when the program is RUNNING.
+    """
+
+    STARTING = b"starting"
+    RUNNING = b"running"
+    STOPPING = b"stopping"