Fix Windows watcher false edits from NTFS atime

[JJordan0C]

Summary

• ignore Windows watcher events when the file's current size and modification time still match its indexed metadata
• preserve deletion handling and fail open when filesystem or database metadata cannot be checked
• add unit coverage plus a Windows-only regression test for NTFS access-time updates
• document the fix in the changelog

Fixes #1451

Validation

• npm run build
• npx vitest run __tests__/watcher.test.ts __tests__/mcp-staleness-banner.test.ts — 40 tests passed on Windows
• real Windows watcher check with DisableLastAccess = 2: an access-time-only update produced no pending edit, while a real write remained detectable
• full Node 22 Linux validation in a clean Docker container: npm ci && npm run build && npm test