Fix cleaning safety guards

[edufalcao]

Summary

• Fix item selection state so items that scan as not selected, especially large and old files, remain deselected unless the user explicitly opts them in.
• Add a destructive confirmation gate for manual cleaning and snapshot the exact selected items at confirmation request time.
• Restrict scheduled auto-cleaning to cache-like categories and keep personal-file/purgeable categories out of unattended cleanup.
• Add XCTest coverage for selection semantics, scheduled-clean category policy, and manual cleaning confirmation behavior.

Safety notes

• This change was prepared by an LLM coding agent, Codex, with human oversight.
• Because this application can permanently delete local files, this PR should be reviewed and tested carefully before merging.
• The cleaner still uses permanent deletion through FileManager.removeItem; this PR reduces accidental deletion risk but does not change deletion to Trash-based recovery.

Verification

• xcodebuild test -project PureMac.xcodeproj -scheme PureMac -destination 'platform=macOS'
  • 9 tests executed, 0 failures, TEST SUCCEEDED.
• xcodebuild build -project PureMac.xcodeproj -scheme PureMac -configuration Release -destination 'platform=macOS'
  • BUILD SUCCEEDED.
• git diff --check
  • No whitespace errors.
• Static searches checked for stale deselectedItems state, telemetry/network clients, credential handling, and destructive/process execution surfaces.