chore: remove trailing slashes from .gitignore entries

[avoidwork]

Description

Standardized .gitignore entries by removing trailing slashes from directory patterns. This is a cosmetic cleanup — both forms are functionally equivalent in git, but consistency matters.

Type of Change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactor (no functional behavior change)
• Performance improvement
• CI / build / tooling

Testing

N/A — purely cosmetic change to .gitignore. No functional impact.

Coverage

• Line coverage maintained

Checklist

• npm run lint passes
• Tests pass with maintained line coverage
• No forbidden patterns used
• Conventional Commit style applied