docs: clean up README instructions

[partyplatter08-lab]

Summary

• Refresh the README setup flow with dependency installation, config copying, required settings, and alias instructions.
• Document the current GitHappens command surface for issue and merge request creation, project selection, metadata flags, review, AI review, summaries, incident reports, and deployment lookup.
• Fix README typos, the config filename reference, the malformed auto-merge example, and the duplicated production deployment section.

Validation

• git diff --check HEAD
• npx --yes markdownlint-cli --disable MD013 MD033 MD041 -- README.md
• python3 -c "import py_compile; py_compile.compile('gitHappens.py', cfile='/tmp/githappens.pyc', doraise=True); py_compile.compile('ai_code_review.py', cfile='/tmp/ai_code_review.pyc', doraise=True)"

Fixes #114