Add deterministic deduplication, rclone backend, and database purge command

- Implement deterministic blob hashing using double SHA256 of uncompressed
  plaintext data, enabling deduplication even after local DB is cleared
- Add Stat() check before blob upload to skip existing blobs in storage
- Add rclone storage backend for additional remote storage options
- Add 'vaultik database purge' command to erase local state DB
- Add 'vaultik remote check' command to verify remote connectivity
- Show configured snapshots in 'vaultik snapshot list' output
- Skip macOS resource fork files (._*) when listing remote snapshots
- Use multi-threaded zstd compression (CPUs - 2 threads)
- Add writer tests for double hashing behavior

internal/cli/remote.go

@@ -0,0 +1,89 @@
+package cli
+
+import (
+	"context"
+	"os"
+
+	"git.eeqj.de/sneak/vaultik/internal/log"
+	"git.eeqj.de/sneak/vaultik/internal/vaultik"
+	"github.com/spf13/cobra"
+	"go.uber.org/fx"
+)
+
+// NewRemoteCommand creates the remote command and subcommands
+func NewRemoteCommand() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "remote",
+		Short: "Remote storage management commands",
+		Long:  "Commands for inspecting and managing remote storage",
+	}
+
+	// Add subcommands
+	cmd.AddCommand(newRemoteInfoCommand())
+
+	return cmd
+}
+
+// newRemoteInfoCommand creates the 'remote info' subcommand
+func newRemoteInfoCommand() *cobra.Command {
+	var jsonOutput bool
+
+	cmd := &cobra.Command{
+		Use:   "info",
+		Short: "Display remote storage information",
+		Long: `Shows detailed information about remote storage, including:
+- Size of all snapshot metadata (per snapshot and total)
+- Count and total size of all blobs
+- Count and size of referenced blobs (from all manifests)
+- Count and size of orphaned blobs (not referenced by any manifest)`,
+		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 || jsonOutput,
+				},
+				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.RemoteInfo(jsonOutput); err != nil {
+										if err != context.Canceled {
+											if !jsonOutput {
+												log.Error("Failed to get remote info", "error", 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
+							},
+						})
+					}),
+				},
+			})
+		},
+	}
+
+	cmd.Flags().BoolVar(&jsonOutput, "json", false, "Output in JSON format")
+
+	return cmd
+}