The --prune flag on 'snapshot create' was accepted but silently did nothing
(TODO stub). This connects it to actually:
1. Purge old snapshots (keeping only the latest) via PurgeSnapshots
2. Remove unreferenced blobs from storage via PruneBlobs
The pruning runs after all snapshots complete successfully, not per-snapshot.
Both operations use --force mode (no interactive confirmation) since --prune
is an explicit opt-in flag.
Moved the prune logic from createNamedSnapshot (per-snapshot) to
CreateSnapshot (after all snapshots), which is the correct location.
clawbot
0b0398b3e9