[ronaldtse]

Summary

bin/lint-no-raw-mdc was a bash script. For a Ruby library this is the
wrong choice — it requires bash on PATH (works on Linux/macOS, and on
Windows only because Git for Windows ships bash), and the previous PR
had to special-case the Rakefile to invoke bash bin/lint-no-raw-mdc
explicitly.

Change

Rewrote bin/lint-no-raw-mdc as a Ruby script:

• Shebang is now #!/usr/bin/env ruby
• Uses Open3.capture3 to invoke git grep
• Filter logic (excluded paths, comment-line skip) is plain Ruby
• POSIX ERE source string declared as a constant — git grep -E
  doesn't accept Ruby regex syntax like \d or (?:...)
• Exit codes preserved: 0 on clean, 1 on violation, 2 on git grep
  internal failure

Rakefile reverted to ruby "bin/lint-no-raw-mdc" — the previous
bash bin/lint-no-raw-mdc workaround is no longer needed. Ruby is
guaranteed on PATH because Rake itself runs on Ruby.

Verified locally

• bundle exec rake lint:registry — passes on a clean tree
• Planted "MDC_P999" in a tracked file under lib/opencdd/entity/ —
  the script reports the violation with exit 1, matching the previous
  bash behavior
• Clean tree — exit 0

Test plan

• Local: rake lint passes on main
• Local: planted violation is detected
• CI: all 10 jobs green (3.3, 3.4, 4.0 × macOS, Ubuntu, Windows)