Consolidate CLI verbs; retire overlapping commands

The verb surface accumulated overlapping cleanup commands. Consolidate
so each cleanup verb has one meaning:

- Rename 'database purge' -> 'database delete'. The command removes the
  SQLite file entirely; "purge" wrongly suggested purging contents.
- Fold 'snapshot cleanup' into 'prune'. Prune now runs three passes:
  reconcile local snapshots against the remote (previously the
  standalone cleanup command), drop orphaned local rows, then delete
  unreferenced remote blobs. One command, one mental model.
- Delete 'store info'. Its output was a strict subset of 'remote info',
  which already prints storage type + location. Any user reaching for
  either should reach for 'remote info'.
- Drop 'snapshot remove --all'. It duplicated 'remote nuke --force'.
  'remote nuke' is the single supported entry point for wiping the
  destination store.

Also update the storage-binding error message to reference the new
'vaultik database delete' name.

internal/vaultik/storage_bind.go

@@ -86,6 +86,6 @@ func buildBindingMismatchMessage(stored, configured string) string {
 		"\n" +
 		"To proceed, either:\n" +
 		"  - revert storage_url in your config to the bound destination, or\n" +
-		"  - run 'vaultik database purge' to discard the local index and rebuild it\n" +
+		"  - run 'vaultik database delete' to discard the local index and rebuild it\n" +
 		"    from a fresh full backup against the new destination"
 }