[TASK] js.node_modules-lite scanner (FastWalker(package.json))

[kirich1409]

Context

Walk projectRoots looking for package.json. For each project, locate sibling node_modules/ and filter by mtime cold > N days.

Acceptance criteria

• Scanner emits .directory items for cold node_modules only.

Files to touch (estimate)

best-effort estimate; agent refines during implementation

Implementation notes

n/a

Dependencies

• Blocked by [TASK] ProjectMarker.predicate case #61

Safety checklist

See .github/ISSUE_TEMPLATE/task.yml — tick applicable invariants in the issue if any destructive path is touched.

Definition of Done

• Acceptance criteria satisfied and verifiable
• Tests added or updated
• No build / lint / test regressions
• Self-review against research-report invariants
• Code review approved