docs: add docs to CB

Pretty much every class and method should have documentation now.

ref: N25B-295

src/control_backend/api/v1/endpoints/robot.py

@@ -17,6 +17,16 @@ router = APIRouter()
 
 @router.post("/command", status_code=202)
 async def receive_command(command: SpeechCommand, request: Request):
+    """
+    Send a direct speech command to the robot.
+
+    Publishes the command to the internal 'command' topic. The
+    :class:`~control_backend.agents.actuation.robot_speech_agent.RobotSpeechAgent`
+    will forward this to the robot.
+
+    :param command: The speech command payload.
+    :param request: The FastAPI request object.
+    """
     # Validate and retrieve data.
     SpeechCommand.model_validate(command)
     topic = b"command"
@@ -29,12 +39,22 @@ async def receive_command(command: SpeechCommand, request: Request):
 
 @router.get("/ping_check")
 async def ping(request: Request):
+    """
+    Simple HTTP ping endpoint to check if the backend is reachable.
+    """
     pass
 
 
 @router.get("/ping_stream")
 async def ping_stream(request: Request):
-    """Stream live updates whenever the device state changes."""
+    """
+    SSE endpoint for monitoring the Robot Interface connection status.
+
+    Subscribes to the internal 'ping' topic (published by the RI Communication Agent)
+    and yields status updates to the client.
+
+    :return: A StreamingResponse of connection status events.
+    """
 
     async def event_stream():
         # Set up internal socket to receive ping updates