ci: eject from projen

[tompahoward]

Summary

• Eject from projen to remove generated-file management overhead
• Replace all npx projen scripts with direct commands in package.json
• Remove .projenrc.ts, .projen/, and @mountainpass/cool-bits-for-projen dependency
• Upgrade all GitHub Actions from deprecated v2/v3 to v4
• Replace npm pack command with version compatible with newer npm
• Update CI workflows to use npm run directly instead of projen task runner

Risk

• Release workflow: Replaced projen's bump/unbump builtins with npx standard-version — needs manual verification before first release
• Irreversible: Cannot easily return to projen-managed config after merge

Test plan

• All tests pass (5/5, 100% coverage)
• Lint, spellcheck, and eslint:json all pass
• dry-aged-deps --check passes
• Pre-push hook works end-to-end
• Verify release workflow with a dry run (manual step)

Depends on: #45

https://claude.ai/code/session_01HNvBcQzT1SviRqkUpP5Xce

[mergify]

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Details

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