docs: add docs to CB

Pretty much every class and method should have documentation now.

ref: N25B-295

src/control_backend/schemas/belief_message.py

@@ -2,10 +2,22 @@ from pydantic import BaseModel
 
 
 class Belief(BaseModel):
+    """
+    Represents a single belief in the BDI system.
+
+    :ivar name: The functor or name of the belief (e.g., 'user_said').
+    :ivar arguments: A list of string arguments for the belief.
+    :ivar replace: If True, existing beliefs with this name should be replaced by this one.
+    """
+
     name: str
     arguments: list[str]
     replace: bool = False
 
 
 class BeliefMessage(BaseModel):
+    """
+    A container for transporting a list of beliefs between agents.
+    """
+
     beliefs: list[Belief]