docs: add docs to CB

Pretty much every class and method should have documentation now.

ref: N25B-295

src/control_backend/agents/llm/llm_instructions.py

@@ -1,7 +1,12 @@
 class LLMInstructions:
     """
-    Defines structured instructions that are sent along with each request
-    to the LLM to guide its behavior (norms, goals, etc.).
+    Helper class to construct the system instructions for the LLM.
+
+    It combines the base persona (Pepper robot) with dynamic norms and goals
+    provided by the BDI system.
+
+    :ivar norms: A list of behavioral norms.
+    :ivar goals: A list of specific conversational goals.
     """
 
     @staticmethod
@@ -17,14 +22,22 @@ class LLMInstructions:
             "Try to learn the user's name during conversation.",
         ]
 
-    def __init__(self, norms: list[str] = None, goals: list[str] = None):
+    def __init__(self, norms: list[str] | None = None, goals: list[str] | None = None):
         self.norms = norms or self.default_norms()
         self.goals = goals or self.default_goals()
 
     def build_developer_instruction(self) -> str:
         """
-        Builds a multi-line formatted instruction string for the LLM.
-        Includes only non-empty structured fields.
+        Builds the final system prompt string.
+
+        The prompt includes:
+        1.  Persona definition.
+        2.  Constraint on response length.
+        3.  Instructions on how to handle goals (reach them in order, but prioritize natural flow).
+        4.  The specific list of norms.
+        5.  The specific list of goals.
+
+        :return: The formatted system prompt string.
         """
         sections = [
             "You are a Pepper robot engaging in natural human conversation.",