feat: per-name purge filtering for snapshot purge

PurgeSnapshots now applies --keep-latest retention per snapshot name
instead of globally across all names. Previously, --keep-latest would
keep only the single most recent snapshot regardless of name, deleting
the latest snapshots of other names (e.g. keeping only the newest
'system' snapshot while deleting all 'home' snapshots).

Changes:
- Add parseSnapshotName() to extract snapshot name from snapshot IDs
- Add SnapshotPurgeOptions struct with Name field for --name filtering
- Add PurgeSnapshotsWithOptions() method accepting full options
- Modify --keep-latest to group snapshots by name and keep the latest
  per group (backward compatible: PurgeSnapshots() wrapper preserved)
- Add --name flag to both 'vaultik purge' and 'vaultik snapshot purge'
  CLI commands to filter purge operations to a specific snapshot name
- Add comprehensive tests for per-name purge behavior including:
  multi-name retention, name filtering, legacy/mixed format support,
  older-than with name filter, and edge cases

closes #9

internal/cli/purge.go

@@ -11,16 +11,9 @@ import (
 	"go.uber.org/fx"
 )
 
-// PurgeOptions contains options for the purge command
-type PurgeOptions struct {
-	KeepLatest bool
-	OlderThan  string
-	Force      bool
-}
-
 // NewPurgeCommand creates the purge command
 func NewPurgeCommand() *cobra.Command {
-	opts := &PurgeOptions{}
+	opts := &vaultik.SnapshotPurgeOptions{}
 
 	cmd := &cobra.Command{
 		Use:   "purge",
@@ -28,8 +21,15 @@ func NewPurgeCommand() *cobra.Command {
 		Long: `Removes snapshots based on age or count criteria.
 
 This command allows you to:
-- Keep only the latest snapshot (--keep-latest)
+- Keep only the latest snapshot per name (--keep-latest)
 - Remove snapshots older than a specific duration (--older-than)
+- Filter to a specific snapshot name (--name)
+
+When --keep-latest is used, retention is applied per snapshot name. For example,
+if you have snapshots named "home" and "system", --keep-latest keeps the most
+recent of each.
+
+Use --name to restrict the purge to a single snapshot name.
 
 Config is located at /etc/vaultik/config.yml by default, but can be overridden by 
 specifying a path using --config or by setting VAULTIK_CONFIG to a path.`,
@@ -66,7 +66,7 @@ specifying a path using --config or by setting VAULTIK_CONFIG to a path.`,
 								// Start the purge operation in a goroutine
 								go func() {
 									// Run the purge operation
-									if err := v.PurgeSnapshots(opts.KeepLatest, opts.OlderThan, opts.Force); err != nil {
+									if err := v.PurgeSnapshotsWithOptions(opts); err != nil {
 										if err != context.Canceled {
 											log.Error("Purge operation failed", "error", err)
 											os.Exit(1)
@@ -92,9 +92,10 @@ specifying a path using --config or by setting VAULTIK_CONFIG to a path.`,
 		},
 	}
 
-	cmd.Flags().BoolVar(&opts.KeepLatest, "keep-latest", false, "Keep only the latest snapshot")
+	cmd.Flags().BoolVar(&opts.KeepLatest, "keep-latest", false, "Keep only the latest snapshot per name")
 	cmd.Flags().StringVar(&opts.OlderThan, "older-than", "", "Remove snapshots older than duration (e.g. 30d, 6m, 1y)")
 	cmd.Flags().BoolVar(&opts.Force, "force", false, "Skip confirmation prompts")
+	cmd.Flags().StringVar(&opts.Name, "name", "", "Filter purge to a specific snapshot name")
 
 	return cmd
 }