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

CLAUDE.md

@@ -18,16 +18,16 @@ uv run pytest            # run tests
 ## Code quality
 
 Pre-commit hooks run automatically on `git commit`:
-- **pyright** - static type checking (config: `pyrightconfig.json` points to `.devenv/state/venv`)
+- **basedpyright** - strict static type checking (config: `pyrightconfig.json` points to `.devenv/state/venv`)
 - **ruff check** - linting with auto-fix
 - **ruff format** - formatting
 - **commitizen** - enforces conventional commit messages (`feat:`, `fix:`, `chore:`, etc.)
 
 Run manually:
 ```bash
-/nix/store/h7f5vym2ykpl7ls8icw0wiqgmv9xiwnx-pyright-1.1.407/bin/pyright
-/nix/store/xmy9vff4zlbvkz3y830085dzgjpmaj8d-ruff-0.14.14/bin/ruff check
-/nix/store/xmy9vff4zlbvkz3y830085dzgjpmaj8d-ruff-0.14.14/bin/ruff format --check
+basedpyright
+ruff check
+ruff format --check
 ```
 
 ## Code style conventions
@@ -110,9 +110,10 @@ The provider writes the result file to `project_dir / target_name`.
 ## Dependencies
 
 - `typer` - CLI framework
-- `pydantic` / `pydantic-settings[yaml]` - config parsing (pyyaml comes via the yaml extra)
+- `pydantic` - data validation and config models
+- `pyyaml` - YAML parsing
 - `networkx` - dependency graph
-- `blackforest` - BlackForestLabs API client (sync, uses `requests`)
+- `blackforest` - BlackForestLabs API client (sync, uses `requests`; no type stubs)
 - `mistralai` - Mistral API client (supports async)
 - `httpx` - async HTTP for downloading BFL result images (transitive via mistralai)
 - `hatchling` - build backend