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/config.py

@@ -78,5 +78,5 @@ def resolve_model(target_name: str, target: TargetConfig, defaults: Defaults) ->
 def load_config(config_path: Path) -> ProjectConfig:
     """Load and validate a ``.bulkgen.yaml`` file."""
     with config_path.open() as f:
-        raw = yaml.safe_load(f)
+        raw = yaml.safe_load(f)  # pyright: ignore[reportAny]
     return ProjectConfig.model_validate(raw)