This PR addresses the security and reliability improvements outlined in issue #1975.

## Changes Made

### High Priority - Security
1. **Remove eval from bin/ci-rerun-failures**
   - Replaced `eval` usage with a safe `run_command()` function using case statement
   - Commands are now explicitly defined in case branches, eliminating potential injection risks
   - Maintains same functionality while being more maintainable and secure

### Medium Priority - Documentation
2. **Document Ruby version requirement in bin/ci-switch-config**
   - Added comment explaining that script/convert uses current Ruby in PATH
   - Documents that version manager may not have reloaded yet
   - Specifies Ruby 2.6+ compatibility requirement

### Low Priority - Reliability
3. **Add bounds check for array access in bin/ci-run-failed-specs**
   - Added defensive check before accessing UNIQUE_SPECS[0]
   - Prevents potential errors if array is empty

4. **Improve git restore error handling in bin/ci-switch-config**
   - Replaced silent failure (2>/dev/null || true) with explicit warning
   - Users now see a clear message if files cannot be restored
   - Differentiates between success and partial failure

## Testing
- All scripts validated with `bash -n` for syntax errors
- RuboCop linting passed with zero offenses
- Code formatted with Prettier

Fixes #1975

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Co-Authored-By: Claude <[email protected]>