Update website documentation to reflect current Echo v4 state

[vishr]

Summary

• Updated Go version requirement from 1.13 to 1.20 to match current project state
• Enhanced Hello World example with proper middleware setup (Logger, Recover)
• Improved introduction to focus on examples repository purpose rather than framework docs
• Added comprehensive example categorization and better resource links
• Enhanced graceful shutdown documentation with implementation details and key features
• Improved JWT authentication cookbook with clearer feature descriptions
• Added CLAUDE.md file for future Claude Code development guidance

Test plan

• [ ] Verify documentation renders correctly on the website
• [ ] Check that all links are working properly
• [ ] Ensure Go version requirements are consistent across docs
• [ ] Validate that examples still work with updated documentation

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