revert: switch helper LLM back to haiku 4.5

src/mnemosyne/helper_llm.py

@@ -155,7 +155,7 @@ class HelperLLM:
     def __init__(
         self,
         api_key: str | None = None,
-        model: str = "claude-sonnet-4-6-20260217",
+        model: str = "claude-haiku-4-5-20251001",
         base_url: str = "https://api.anthropic.com",
     ) -> None:
         """Initialize the helper LLM client.