refactor(types): auto -> None sweep across entire codebase

Applied 236 return type annotations to functions with no return values
across 100+ files (core modules, tests, scripts, simulations).
Added Phase 4 to python_style_refactor track for remaining 597 items
(untyped params, vars, and functions with return values).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

gemini.py

@@ -11,12 +11,12 @@ def _load_key() -> str:
  with open("credentials.toml", "rb") as f:
   return tomllib.load(f)["gemini"]["api_key"]
 
-def _ensure_client():
+def _ensure_client() -> None:
  global _client
  if _client is None:
   _client = genai.Client(api_key=_load_key())
 
-def _ensure_chat():
+def _ensure_chat() -> None:
  global _chat
  if _chat is None:
   _ensure_client()
@@ -29,7 +29,7 @@ def send(md_content: str, user_message: str) -> str:
  response = _chat.send_message(full_message)
  return response.text
 
-def reset_session():
+def reset_session() -> None:
  global _client, _chat
  _client = None
  _chat = None