[kingchenc]

Comparisons

• Right after a scan the app compares it with the newest earlier snapshot of
  the same folder and shows a "Since last scan" card (total change, new /
  gone / changed files); a click opens the comparison. A Compare button next
  to Rescan does the same for the folder on screen. The changes tab was easy
  to miss at the bottom of the dashboard.
• The current state is captured once per tree under its own mutex, so the
  background snapshot save and the comparison no longer capture it twice.

Duplicates

• The groups were correct (verified independently with SHA-256: e.g. the
  Star Citizen and Predecessor launchers, or one Halo Infinite music bank
  under three names, are byte-identical), but on a games drive nearly all of
  them are copies inside installed programs, which ship them on purpose and
  break when one is deleted.
• Files inside program and game folders (Steam, Epic, Battle.net, Ubisoft,
  EA, Program Files, WindowsApps, AppData, node_modules, ...) or of program /
  game data types (dll, exe, pak, pck, ...) are now marked. Groups made only
  of them are hidden by default (shown with a lock on request) and the KPIs
  split "your files" from "program & game files". While hidden they are
  never removed; in a mixed group the program's copy is kept by default; a
  reclaim touching them asks with an extra warning.
• Folder pairs: which folders share identical files, with group / file
  counts and reclaimable bytes; a click filters the groups to that pair.
• Category filter, an "identical (BLAKE3)" marker with the hash, and a note
  that names do not matter.

UI helper tests: 22 (protected paths, folder pairs).