Release 0.17.1

Added

• build_minimal_strategy() — 4-step pipeline (context → lookup → execute → return) for pre-validated internal hot paths. Registered as "minimal" in Executor preset builders.
• requires / provides on BaseStep — Optional advisory fields declaring step dependencies. ExecutionStrategy validates dependency chains at construction and insertion, emitting warnings for unmet requires.

Fixed

• "minimal" added to preset builders — Executor(strategy="minimal") now works. Previously missing from _resolve_strategy_name() preset dict.
• Executor docstrings updated — Constructor and _resolve_strategy_name docstrings now list all 5 presets (was missing "minimal").

---