Collapse snapshot prune into vaultik prune; auto-clean on removal

The CLI had two commands named "prune" doing different jobs (local
DB orphan cleanup vs. remote blob garbage collection), which was
confusing and forced a manual two-step workflow after deleting any
snapshot.

Single user-facing prune surface is now `vaultik prune`, which calls
PruneDatabase (local orphan cleanup) then PruneBlobs (remote unref
blob GC). Snapshot deletion paths (snapshot remove, snapshot remove
--all, snapshot purge) auto-run CleanupOrphanedData inline so the
local index database doesn't accumulate ghost rows after every
removal — the user observed ~39k orphaned files and 2 orphaned blobs
after a remove --all because that cleanup was previously a separate
opt-in command. `snapshot prune` is removed.

Also addresses the doc/help-string drift the user audit caught:

  * cli/prune.go help text used to reference a non-existent
    `vaultik purge` command.
  * cli/config.go get/set short/long examples were S3-specific
    (s3.bucket) when the primary storage configuration is
    storage_url.
  * vaultik/info.go printed S3 Bucket/Endpoint/Region labels
    unconditionally; for file:// or rclone:// users those rows
    were empty. The Storage Configuration block now prints the
    storer's Type+Location first, the storage_url string when set,
    and only emits S3 rows that are actually populated.
  * vaultik/info.go's "Run 'vaultik prune --remote'" hint
    referenced a flag that doesn't exist.
  * vaultik/blobcache.go's doc comment claimed LRU eviction, which
    is no longer the restore-time policy (the sweeper drives
    eviction; LRU is the safety-net fallback when maxBytes is
    finite).
  * README.md listed `vaultik restore`, `vaultik snapshot prune`,
    and `s3.bucket` example, all out of date.

README's roadmap section is rewritten with concrete pre-1.0 items
(security audit, error-condition tests, parallel blob downloads,
restart of interrupted restore, …) so the next-steps surface
matches what the project actually still needs.

The cleanup calls are guarded against a nil SnapshotManager so
tests that construct a bare Vaultik struct continue to work.

internal/cli/snapshot.go

@@ -25,7 +25,6 @@ func NewSnapshotCommand() *cobra.Command {
 	cmd.AddCommand(newSnapshotPurgeCommand())
 	cmd.AddCommand(newSnapshotVerifyCommand())
 	cmd.AddCommand(newSnapshotRemoveCommand())
-	cmd.AddCommand(newSnapshotPruneCommand())
 	cmd.AddCommand(newSnapshotCleanupCommand())
 	cmd.AddCommand(newSnapshotRestoreCommand())
 
@@ -415,64 +414,6 @@ Use --all --force to remove all snapshots.`,
 	return cmd
 }
 
-// newSnapshotPruneCommand creates the 'snapshot prune' subcommand
-func newSnapshotPruneCommand() *cobra.Command {
-	cmd := &cobra.Command{
-		Use:   "prune",
-		Short: "Remove orphaned data from local database",
-		Long: `Removes orphaned files, chunks, and blobs from the local database.
-
-This cleans up data that is no longer referenced by any snapshot, which can
-accumulate from incomplete backups or deleted snapshots.`,
-		Args: cobra.NoArgs,
-		RunE: func(cmd *cobra.Command, args []string) error {
-			// Use unified config resolution
-			configPath, err := ResolveConfigPath()
-			if err != nil {
-				return err
-			}
-
-			rootFlags := GetRootFlags()
-			return RunWithApp(cmd.Context(), AppOptions{
-				ConfigPath: configPath,
-				LogOptions: log.LogOptions{
-					Verbose: rootFlags.Verbose,
-					Debug:   rootFlags.Debug,
-					Quiet:   rootFlags.Quiet,
-				},
-				Modules: []fx.Option{},
-				Invokes: []fx.Option{
-					fx.Invoke(func(v *vaultik.Vaultik, lc fx.Lifecycle) {
-						lc.Append(fx.Hook{
-							OnStart: func(ctx context.Context) error {
-								go func() {
-									if _, err := v.PruneDatabase(); err != nil {
-										if err != context.Canceled {
-											log.Error("Failed to prune database", "error", err)
-											ReportError("Failed to prune database: %v", err)
-											os.Exit(1)
-										}
-									}
-									if err := v.Shutdowner.Shutdown(); err != nil {
-										log.Error("Failed to shutdown", "error", err)
-									}
-								}()
-								return nil
-							},
-							OnStop: func(ctx context.Context) error {
-								v.Cancel()
-								return nil
-							},
-						})
-					}),
-				},
-			})
-		},
-	}
-
-	return cmd
-}
-
 // newSnapshotCleanupCommand creates the 'snapshot cleanup' subcommand
 func newSnapshotCleanupCommand() *cobra.Command {
 	cmd := &cobra.Command{