chore: make public repository canonical

[danii1]

Summary

• adds public CI for format, lint, typecheck, tests, and builds
• switches PM Desktop releases to the same public repository using GITHUB_TOKEN
• updates contributor and maintainer documentation for the canonical public workflow
• hardens AboutDialog test teardown against asynchronous React Query work after DOM cleanup

Safety and validation

• audited the tracked tree for private paths, secrets, and pull_request_target usage
• repository pre-commit format, lint, and typecheck pass
• repository pre-push test and typecheck pass
• PM Desktop full suite passes repeatedly: 438 tests

The base is the final-sync branch so this PR shows only canonicalization changes; retarget to main after the sync PR merges.