Add contributor-readiness: license, CI, docs, and tests

[lgriffin]

Summary

• Apache 2.0 license added with LICENSE file and pyproject.toml license field
• GitHub Actions CI pipeline (.github/workflows/ci.yml) with lint (ruff + mypy) and test (pytest + coverage) jobs
• Contributor docs: CONTRIBUTING.md (dev setup, branch naming, PR process), CODE_OF_CONDUCT.md (Contributor Covenant v2.1), README.md badges and contributing section
• Pre-commit hooks (.pre-commit-config.yaml): ruff lint/format + standard file checks
• cli.py refactor: extracted _add_analysis_args() to deduplicate 11 shared arguments between analyze and report subcommands
• formatter.py split: monolithic file split into formatter.py (public API + shared helpers), formatter_rich.py, formatter_text.py, formatter_json.py
• 401 new tests: test_token_counting.py (45), test_validation.py (82), test_waste_detectors.py (64) — plus expanded coverage from background agents. Total: 857 passing (up from 456)

Test plan

• Full test suite: 857 passed, 1 pre-existing failure (unrelated deduplication BDD step)
• Verified pre-existing failure exists on clean main (not introduced by this PR)
• ruff check src/ passes
• All three formatter dispatch paths (rich/text/json) exercised by existing tests

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