Extract filesystem selector matching

[autholykos]

Summary

• extract shared pathselector validation and recursive matching for filesystem source selectors
• route config validation and source selection through the same selector contract
• move low-level selector matcher tests into the new package while keeping source integration coverage

Tests

• go test ./...

[Copilot]

Pull request overview

Extracts filesystem source selector validation and recursive matching into a shared internal/pathselector package, then reuses that contract from both config validation and source selection explanation, while relocating low-level matcher tests into the new package.

Changes:

• Introduce internal/pathselector with Compile/Validate/Match and recursive ** matching.
• Route filesystem selector validation in config through pathselector.Validate.
• Update source explanation matching to use pathselector.Match and move relevant tests to the new package.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/source/filesystem_test.go	Removes selector/matcher unit tests that are now owned by internal/pathselector.
internal/source/explain.go	Switches selector matching to pathselector.Match and removes inlined matcher implementation.
internal/pathselector/pathselector.go	Adds the shared selector compiler/validator and recursive matcher.
internal/pathselector/pathselector_test.go	Adds unit tests for recursive matching and validation errors.
internal/config/config.go	Uses pathselector.Validate for filesystem source include/exclude pattern validation.

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