v1.0.3

Add low-priority enhancements and polish

This commit implements 5 low-priority improvements to enhance
documentation, activation handling, and overall plugin polish:

1. Improve GitHub update checker caching strategy
   - Increased cache duration from 6 to 12 hours (configurable constant)
   - Added debug logging for cache operations
   - Better error handling with structured logging
   - Improved handling of API failures and edge cases

2. Add activation/deactivation logic improvements
   - PHP version requirement check (7.2+) on activation
   - WordPress version requirement check (5.0+) on activation
   - Prevent settings overwrite on re-activation
   - Track activation timestamp and version
   - Clear options cache on deactivation
   - Comprehensive logging of activation/deactivation events

3. Complete internationalization (i18n)
   - Wrapped all wp_die() error messages in translation functions
   - Added text domain to all user-facing strings
   - Improved consistency across OIDC and SAML error messages
   - Plugin now fully translatable via .po/.mo files

4. Add CHANGELOG.md file
   - Comprehensive changelog following Keep a Changelog format
   - Documents all versions from 1.0.0 to current
   - Includes security notices and upgrade notes
   - Categorized changes (Added, Changed, Fixed, Security)

5. Enhance inline documentation
   - Added detailed PHPDoc blocks with @since tags
   - Included usage examples in docblocks
   - Better parameter and return value documentation
   - Enhanced class-level documentation
   - Improved method descriptions with context

These changes improve the overall polish and maintainability of the
plugin without affecting functionality.