refactor: switch to basedpyright, remove pydantic-settings

- Replace pyright with basedpyright in devenv.nix (custom hook)
- Add basedpyright to devenv packages
- Fix all basedpyright warnings: add DiGraph[str] type args, annotate
  class attributes, narrow SyncResponse, handle unused call results,
  suppress unavoidable Any from yaml.safe_load and untyped blackforest
- Replace pydantic-settings[yaml] with direct pyyaml dependency
- Update CLAUDE.md to reflect basedpyright and dependency changes

bulkgen/providers/text.py

@@ -14,6 +14,8 @@ from bulkgen.providers import Provider
 class TextProvider(Provider):
     """Generates text via the Mistral API."""
 
+    _api_key: str
+
     def __init__(self, api_key: str) -> None:
         self._api_key = api_key
 
@@ -50,8 +52,8 @@ class TextProvider(Provider):
                 messages=[models.UserMessage(content=full_prompt)],
             )
 
-        if response is None or not response.choices:
-            msg = f"Mistral API returned no response for target '{target_name}'"
+        if not response.choices:
+            msg = f"Mistral API returned no choices for target '{target_name}'"
             raise RuntimeError(msg)
 
         content = response.choices[0].message.content
@@ -60,4 +62,4 @@ class TextProvider(Provider):
             raise RuntimeError(msg)
 
         text = content if isinstance(content, str) else str(content)
-        output_path.write_text(text)
+        _ = output_path.write_text(text)