fix(affected): recognize root-level test files

[Jseca666]

Summary

• reuse the shared isTestFile() classifier in codegraph affected
• recognize root-level pytest files such as tests/test_example.py
• use the existing picomatch dependency for custom --filter globs

Root cause

The affected command maintained a second, narrower set of test-file patterns instead of using the shared classifier. A dependent file such as tests/test_cli.py was present in the graph and traversed, but it was not classified as a test because the CLI-only directory regex required a leading slash and did not recognize Python's test_*.py naming convention.

The hand-written glob conversion also translated ** into one-or-more path characters, so tests/**/*.py failed to match a test directly under tests/.

Verification

• npm run build
• npm test -- __tests__/is-test-file.test.ts __tests__/cli-affected-paths.test.ts
• 8 related tests pass, including end-to-end coverage for root-level pytest files and zero-directory globstar matching