Add Snapper Snapshots extension

[samvoelzke]

Adds Snapper Snapshots — browse, create and inspect Btrfs snapshots managed by Snapper (the engine behind Btrfs Assistant) from Vicinae.

Commands

• Browse Snapshots — list Snapper configs and snapshots, with a decoded, readable changed-files view and on-demand per-file diffs.
• Search Snapshot Files — instant local file search inside any snapshot's read-only mount.
• Create Snapshot — take a new snapshot with a description.

First run

Snapper only allows root to read snapshots by default, so the first open shows a one-tap Set Up Access screen that adds your user to ALLOW_USERS + SYNC_ACL via a single pkexec prompt. After that everything works without further prompts.

Everything runs locally — no network. Full subvolume rollbacks are deliberately left to Btrfs Assistant.