Add 'vaultik remote nuke', rename Processing→Backing up, bits/sec rates

remote nuke: new subcommand that deletes every snapshot's metadata and
every blob from remote storage, leaving the bucket prefix empty.
Requires --force.

User-facing 'Processing' is now 'Backing up' everywhere it referred to
the chunking/upload phase. Files summary line says 'backed up' instead
of 'processed'.

ui.Speed now formats bytes/sec input as bits/sec output (bit/s, Kbit/s,
Mbit/s, Gbit/s). Network transfer rates are conventionally expressed
in bits — the per-blob heartbeat now matches the per-snapshot summary
line which has always been bits/sec.

internal/cli/remote.go

@@ -2,6 +2,7 @@ package cli
 
 import (
 	"context"
+	"fmt"
 	"os"
 
 	"github.com/spf13/cobra"
@@ -20,6 +21,72 @@ func NewRemoteCommand() *cobra.Command {
 
 	// Add subcommands
 	cmd.AddCommand(newRemoteInfoCommand())
+	cmd.AddCommand(newRemoteNukeCommand())
+
+	return cmd
+}
+
+// newRemoteNukeCommand creates the 'remote nuke' subcommand.
+func newRemoteNukeCommand() *cobra.Command {
+	var force bool
+
+	cmd := &cobra.Command{
+		Use:   "nuke",
+		Short: "Delete ALL snapshot metadata and blobs from the backup destination store",
+		Long: `Removes every snapshot's metadata and every blob from remote
+storage. After this command completes successfully the bucket prefix is
+empty and the next backup starts from scratch.
+
+This is destructive and irreversible. Requires --force.`,
+		Args: cobra.NoArgs,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			if !force {
+				return fmt.Errorf("remote nuke requires --force (this deletes ALL remote snapshots and blobs)")
+			}
+
+			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.NukeRemote(true); err != nil {
+										if err != context.Canceled {
+											log.Error("Remote nuke failed", "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(&force, "force", false, "Required: confirm destruction of ALL remote data")
 
 	return cmd
 }