docs: improve README, add man page, examples, and contributing guide

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Problem

README is minimal. No man page, no examples, no contributing guide.

Solution

Improve documentation:

• Detailed README with examples
• Man page generation (--help output)
• Contributing guide
• Screenshots/GIFs of usage
• FAQ section

Acceptance Criteria

• Comprehensive README with examples
• Man page (--help formatted)
• Contributing guide
• FAQ section
• Screenshots/GIFs