Update documentation to v1.1.20 with current features

- Updated all version references to 1.1.20
- Updated WordPress requirement to 6.0+ (tested up to 6.9.x)
- Updated WooCommerce requirement to 8.0+ (tested up to 10.x)
- Added comprehensive file structure showing Twig templates
- Added WooCommerce Blocks compatibility documentation
- Added tier labels feature documentation (v1.1.7)
- Added quantity restrictions feature documentation (v1.1.0)
- Added new usage examples for tier labels and quantity restrictions
- Updated INSTALLATION.md with complete directory structure
- Updated README.md with current version changelog
- Updated QUICKSTART.md with 8 pro tips including new features
- Updated USAGE_EXAMPLES.md with 6 complete examples
- Documented WooCommerce Blocks support and v1.1.20 critical fix

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -301,7 +301,7 @@ sha256sum wc-tier-and-package-prices-X.X.X.zip > wc-tier-and-package-prices-X.X.
 
 ### What's Excluded
 - Git metadata (`.git/`)
-- Development files (`.vscode/`, `.idea/`, `.claude/`, `CLAUDE.md`)
+- Development files (`.vscode/`, `.claude/`, `CLAUDE.md`)
 - Logs and cache files
 - Previous releases
 - `composer.lock` (but `vendor/` is included)