"""Plugin SDK module.

Responsibility: provide extensibility through plugins without
modifying core code.

Future plugin types (per SPEC.md §24):
- DSP Plugin
- Semantic Plugin
- Embedding Plugin
- Recommendation Plugin
- Import Plugin
- Export Plugin
- Visualization Plugin

Plugin lifecycle: Load → Validate → Register → Initialize → Execute → Dispose.
Plugins may be disabled.  The core system must remain operational.
"""