feat: add example catalog and initial examples for ExpressoTS v4

[rsaz]

• Introduced CATALOG.md to list runnable examples for ExpressoTS v4.0.
• Added 15 example projects demonstrating various features including JWT authentication, database integration, and file uploads.
• Created CI workflow for testing all examples on push and pull request events.
• Updated README.md to reference the new catalog and provide quick start instructions.
• Added .env.example and .gitignore files for each example project to standardize environment configuration and ignore unnecessary files.

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