Replace inline `.toISOString().split('T')[0]` pattern with getDbDateStr()
utility across production code, tests, and plugin examples.
Changes:
- Production: 6 files (plugin-bridge, metrics, counters, task-repeat-cfg)
- Tests: 4 spec files (helper functions and direct uses)
- Plugin example: Added formatDateStr() helper matching main app pattern
This ensures consistent local timezone handling for all user-facing date
operations and provides a single source of truth for date string formatting.
- Add @super-productivity/plugin-api package with TypeScript definitions
- Define core plugin interfaces, types, and manifest structure
- Add plugin hooks system for event-driven architecture
- Create plugin API type definitions and constants
- Add documentation and development guidelines
