test: add unit tests for internal/patterns and internal/gitignore

[puremachinery]

Context

internal/patterns currently has no tests, and internal/gitignore also has no test file.

These two packages are not the same kind of test target:

• internal/patterns is straightforward pure matching logic
• internal/gitignore is a thin wrapper around git check-ignore plus an in-memory cache

That means the tests should reflect the real implementation rather than treating both packages as pure parsers.

Proposed change

Add test coverage for both packages.

internal/patterns

Cover:

• Basic glob matching
• Recursive ** behavior
• * and ? matching
• Empty-pattern behavior and other edge cases

internal/gitignore

Cover:

• Behavior against a temporary git repo with real .gitignore files
• Ignored vs non-ignored paths using git check-ignore
• Behavior when git is unavailable or unusable, if practical to simulate
• Cache behavior at a basic level (for example, repeated calls for the same repo root)

Use Go's built-in testing package.

Why this is a good first issue

• The scope is still fairly self-contained
• internal/patterns is an especially approachable unit-test target
• internal/gitignore is a good introduction to how this repo wraps existing system tools

Relevant files

• internal/patterns/
• internal/gitignore/