Fix diff filtering for uppercase extensions and recursive patterns

[a3ylf]

brief diff drops R, R Markdown, and mkmf detections when changed files have uppercase extensions or match a recursive pattern across multiple directories. Normalize pattern extensions to match the changed-extension lookup, and reuse the existing recursive path matcher.

Adds regression coverage for nested .R and .Rmd files, zero/deep ** matches, and ordinary wildcard matches and misses. Both new tests fail before the fix and pass afterward.

Fixes #176.

Validation: go build ./..., go test -race ./..., and golangci-lint 2.13.2 (0 issues).

Prepared with AI assistance.

[abhinavgautam01]

Reviewed the implementation and regression coverage. Both fixes address #176 correctly, including deeply nested paths and zero-directory ** matches. I verified that the new tests fail before the fix and pass afterward...

[Copilot]

🟢 Approval recommended

The filtering fixes and regression coverage are complete with no unresolved blocking issues.

Pull request overview

Fixes brief diff filtering for uppercase extensions and recursive glob patterns.

Changes:

• Normalizes detection pattern extensions.
• Reuses recursive path matching.
• Adds regression tests for nested and wildcard paths.

File summaries

File	Description
detect/filter.go	Corrects extension and recursive-pattern matching.
detect/filter_test.go	Adds regression coverage for updated filtering.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Lite

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