feat: prune backups of uninstalled apps during incremental backup

[mvanhorn]

Summary

Adds an opt-in prune_uninstalled setting so a re-run of backup also reflects app removals, not just additions. When enabled, after a backup completes the script compares the backed-up app folders against the live installed-package list and offers to delete the backups of apps that have been uninstalled since the last run (folder + its appList.txt entry).

• New config flag prune_uninstalled (default 0, off) in both update_backup_settings_conf (tools/tools.sh) and backup_settings.conf.
• New prune_uninstalled_backups() reuses the existing detection idiom from get_name (PackageName-vs-$Apk_info diff) and the existing per-name folder + appList.txt deletion idiom.
• Wired into the real backup path: it runs at the end of a full backup and before the incremental "no app updated" early-exit, so uninstall-only changes are still pruned on a no-op incremental run.

Why this matters

Per #124, re-running a backup today adds newly installed apps but never drops the stored copy of an app that was uninstalled since the last run, so a later restore re-installs apps the user removed. This implements the reporter's requested behavior (compare previous vs current app set, drop backups of apps no longer installed).

Safety:

• Opt-in and default-off — existing users see no behavior change.
• Two-step confirmation before any deletion (matches the script's existing destructive-delete convention); declining deletes nothing.
• Parse-failure protection — a folder whose package name cannot be resolved is skipped, never deleted.
• Local-only — only the local backup is pruned. Streaming-upload mode is skipped (no local files), and when a remote target is configured the run prints a notice that remote directories are not touched.

Testing

• bash -n tools/tools.sh passes.
• Manual reasoning against the scenarios in the issue:
  • device has B C D E F, backup dir has A B C D E F, prune_uninstalled=1 → A's folder and its appList.txt line are removed after confirmation.
  • prune_uninstalled=0 (default) → uninstalled app's backup retained as today, no prompt.
  • no orphans → "nothing to prune", backup untouched.
  • confirmation declined → no folders deleted.
  • unresolvable package name → folder skipped (protected).

Fixes #124

[YAWAsau]

The script is currently undergoing extensive refactoring and feature additions. I will merge this commit once it is stable.