Docs overhaul

[karolswdev]

Title: docs(readme): streamline OSS README, add CLI docs, examples, and coverage

Summary

• Replace long, open-ended README with a concise, OSS‑friendly version: clear “Why”, quick
  install/config, 30‑second example, usage overview, and links to docs.
• Add CLI reference and richer examples (custom fields, sample state) to help users adopt
  the correct TICKET format and understand state/conflicts.
• Add Codecov integration and coverage badge.

Changes

• User-facing docs updated (README/docs)
  • README now includes clickable repo links and light, tasteful emojis.
  • New docs/CLI.md: commands, flags, examples, and conflict strategies.
  • New examples/tickets_with_custom_fields.md and examples/ticketr_state.example.json.
• CI green
  • ci.yml now uploads coverage.out to Codecov using codecov/codecov-action@v4.
  • Coverage badge added to README.
• Tests added/updated (docs/CI-only change; no code logic changed)

Checklist

• I read the Code of Conduct
• I followed the contributing guidelines
• I added a clear description and screenshots/logs/links where helpful

Notes

• Repo hygiene: archived phase docs to docs/archive/, ignored repomix-output.xml and
  phase-*.md.
• Go badge reflects 1.24+.
• Optional future improvements:
  • Enable OpenSSF Scorecard and add badge.
  • Publish Docker image and add Docker badges when ready.

Setup note

• If the repository is private, add CODECOV_TOKEN in repo secrets to enable Codecov
  uploads. Public repos typically work without a token.