Update documentation for lib/ submodule location

- Update file structure in README.md and CLAUDE.md
- Document lib/ directory for git submodules
- Update submodule instructions with relative URL
- Add key learnings about vendor/ vs lib/ conflict

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

README.md

@@ -154,8 +154,9 @@ wc-tier-and-package-prices/
 │   ├── wc-tier-package-prices.pot    # Translation template
 │   ├── wc-tier-package-prices-*.po   # Translation sources
 │   └── wc-tier-package-prices-*.mo   # Compiled translations
-├── vendor/                            # Composer dependencies
-│   └── magdev/wc-licensed-product-client/ # License client (git submodule)
+├── lib/                               # Bundled libraries (git submodules)
+│   └── wc-licensed-product-client/    # License client library
+├── vendor/                            # Composer dependencies (generated)
 ├── CHANGELOG.md                       # Complete version history
 ├── INSTALLATION.md                    # Installation guide
 ├── QUICKSTART.md                      # Quick start guide