docs: add docs to CB

Pretty much every class and method should have documentation now.

ref: N25B-295

src/control_backend/schemas/ri_message.py

@@ -5,16 +5,34 @@ from pydantic import BaseModel
 
 
 class RIEndpoint(str, Enum):
+    """
+    Enumeration of valid endpoints for the Robot Interface (RI).
+    """
+
     SPEECH = "actuate/speech"
     PING = "ping"
     NEGOTIATE_PORTS = "negotiate/ports"
 
 
 class RIMessage(BaseModel):
+    """
+    Base schema for messages sent to the Robot Interface.
+
+    :ivar endpoint: The target endpoint/action on the RI.
+    :ivar data: The payload associated with the action.
+    """
+
     endpoint: RIEndpoint
     data: Any
 
 
 class SpeechCommand(RIMessage):
+    """
+    A specific command to make the robot speak.
+
+    :ivar endpoint: Fixed to ``RIEndpoint.SPEECH``.
+    :ivar data: The text string to be spoken.
+    """
+
     endpoint: RIEndpoint = RIEndpoint(RIEndpoint.SPEECH)
     data: str