fix(batch-lint): keep files with notAppliedFixes (#86)

[luojiyin1987]

Closes #86.

Summary

• batchLint no longer drops files whose lintResult is empty but whose fixedResult.notAppliedFixes is non-empty. The filter now retains an item when it has lint findings or leftover unapplied fixes.
• Extracted the condition into a pure, exported keepLintItem predicate so it is unit-testable without a real worker (same approach as getUnappliedFixesWarnings from feat(fix-mode): warn to stderr when fixes not applied (#85) #89).
• Complements the feat(fix-mode): warn to stderr when fixes not applied (#85) #89 stderr warning: getUnappliedFixesWarnings iterates the batchLint output, so keeping these items ensures the warning actually fires for them.

Verification

• npm run build (tsc cjs + esm) passes.
• npm test: 10 suites / 100 tests pass (4 new keepLintItem unit tests).

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