fix(ruby): run extensionless rdbg scripts through Ruby on Windows

[debugmcpdev]

📋 Description

Windows RubyInstaller installs both a .bat/.cmd shim and an extensionless Ruby script for
rdbg. The adapter already routed shims through Ruby, but an explicit RDBG_PATH that resolved
directly to the extensionless script was passed to spawn() and failed with ENOENT.

This change:

• launches an existing absolute extensionless rdbg script as ruby <script> ... on Windows;
• preserves the existing shim, executable, missing-path, argument, and non-Windows behavior;
• adds regression coverage plus Ruby guide and changelog updates.

Closes #508

🔄 Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• 📚 Documentation update
• 🧪 Test improvement

✅ Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules (not applicable)

🧪 Testing

pnpm --filter @debugmcp/adapter-ruby build
pnpm build
pnpm test:unit
pnpm lint
pnpm check:all-personal-paths

Also exercised tests/e2e/mcp-server-smoke-ruby.test.ts twice through the MCP interface:

• with RDBG_PATH pointing to an isolated extensionless rdbg script with no adjacent shim
  (red before the fix, green after it);
• with RDBG_PATH=C:\Ruby34-x64\bin\rdbg, covering breakpoint binding, locals, expression
  evaluation, stepping, continue, output, environment, and cwd behavior.

Test configuration:

• Windows NT 10.0.26200
• Node.js 24.14.1
• pnpm 10.33.0
• Ruby 3.4.9
• debug/rdbg 1.11.0

📝 Additional Notes

No MCP tool schema or public adapter API changes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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