feat(engine): extract path-matchers.ts's pure classifier family to gittensory-engine

[JSONbored]

Found during a 2026-07-08 miner-roadmap audit: the natural next sibling extraction to the already-shipped test-evidence classifier.

src/signals/path-matchers.ts's matcher family — classifyChangedFile, isGeneratedFile, isVendoredFile, isLockfile, isMinifiedFile, isDocsFile, isDependencyManifestFile, isConfigFile, isNonSubstantivePaddingFile — is 100% pure. Its only import is ./test-evidence, which is already extracted to packages/gittensory-engine/src/signals/test-evidence.ts. The file's own header comment already documents portability discipline ("MUST NOT import from local-branch.ts... reachable from apps/gittensory-ui"), meaning it was written with exactly this kind of extraction in mind.

This is also a direct prerequisite for the separate slop-scoring extraction issue, which depends on this landing first.

Deliverables

• Move the matcher family to packages/gittensory-engine/src/signals/path-matchers.ts
• src/signals/path-matchers.ts becomes a thin re-export shim, matching src/scoring/preview.ts's existing pattern
• Export from the package's public entrypoint (barrel + exports map subpath, matching ./signals/test-evidence's existing precedent)
• Existing test/unit/*.test.ts coverage for path-matchers passes unmodified against the moved implementation

References

• src/signals/path-matchers.ts (source to move, including its own portability-discipline header comment)
• packages/gittensory-engine/src/signals/test-evidence.ts (the extraction pattern to mirror exactly)
• packages/gittensory-engine/package.json (exports map — add the new subpath)

[linear-code]

JSO-3240