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/state.py

@@ -46,7 +46,7 @@ def load_state(project_dir: Path) -> BuildState:
     if not state_path.exists():
         return BuildState()
     with state_path.open() as f:
-        raw = yaml.safe_load(f)
+        raw = yaml.safe_load(f)  # pyright: ignore[reportAny]
     if raw is None:
         return BuildState()
     return BuildState.model_validate(raw)