TypeScript Rewrite: Version Conflict Check

[d4mation]

🎫 ENG-219

Summary

• Adds the built-in version-conflict check that verifies all configured version files contain the same version number
• File existence validation before running the check
• Normalized version comparison (trims beyond 3 segments)
• Registers check:version-conflict subcommand (available even when not configured in .puprc)

Dependencies

• Depends on TypeScript Rewrite: Check Command Infrastructure #50

Test plan

• Automated tests pass (bun run test)
• bun run build succeeds
• bun run lint passes
• bun run typecheck passes
• Configure multiple version files in .puprc paths.versions with matching versions and verify bunx pup check reports no conflicts
• Configure version files with mismatched versions and verify the check fails with a red "Found more than one version" message
• Run bunx pup check:version-conflict and verify it runs standalone without the [version-conflict] prefix
• Run bunx pup check:version-conflict when version-conflict is not in .puprc checks and verify it still runs (built-in always registered)
• Point a version file to a non-existent file and verify it shows a plain ERROR: Version file does not exist message