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/vaultik/prune.go

@@ -15,6 +15,31 @@ type PruneOptions struct {
 	JSON  bool
 }
 
+// NukeRemote deletes every snapshot's metadata and every blob from remote
+// storage. After this returns successfully the bucket prefix is empty and
+// the next backup starts from scratch.
+//
+// Refuses to run unless force is true. The caller is responsible for
+// confirming with the user.
+func (v *Vaultik) NukeRemote(force bool) error {
+	if !force {
+		return fmt.Errorf("nuke requires --force (this deletes ALL remote snapshots and blobs)")
+	}
+
+	v.UI.Begin("Removing all snapshot metadata from backup destination store.")
+	if _, err := v.RemoveAllSnapshots(&RemoveOptions{Force: true, Remote: true}); err != nil {
+		return fmt.Errorf("removing all snapshots: %w", err)
+	}
+
+	v.UI.Begin("Removing all blobs from backup destination store.")
+	if err := v.PruneBlobs(&PruneOptions{Force: true}); err != nil {
+		return fmt.Errorf("pruning blobs: %w", err)
+	}
+
+	v.UI.Complete("Backup destination store is now empty.")
+	return nil
+}
+
 // PruneBlobsResult contains the result of a blob prune operation
 type PruneBlobsResult struct {
 	BlobsFound   int   `json:"blobs_found"`

internal/vaultik/snapshot.go

@@ -306,23 +306,13 @@ func (v *Vaultik) finalizeSnapshotMetadata(snapshotID string, stats *snapshotSta
 	return nil
 }
 
-// formatUploadSpeed formats bytes uploaded and duration into a human-readable speed string
-func formatUploadSpeed(bytesUploaded int64, duration time.Duration) string {
+// uploadSpeed returns the average network upload rate as a colorized
+// bits/sec string, or "N/A" when there's no usable data.
+func (v *Vaultik) uploadSpeed(bytesUploaded int64, duration time.Duration) string {
 	if bytesUploaded <= 0 || duration <= 0 {
-		return "N/A"
-	}
-	bytesPerSec := float64(bytesUploaded) / duration.Seconds()
-	bitsPerSec := bytesPerSec * 8
-	switch {
-	case bitsPerSec >= 1e9:
-		return fmt.Sprintf("%.1f Gbit/s", bitsPerSec/1e9)
-	case bitsPerSec >= 1e6:
-		return fmt.Sprintf("%.0f Mbit/s", bitsPerSec/1e6)
-	case bitsPerSec >= 1e3:
-		return fmt.Sprintf("%.0f Kbit/s", bitsPerSec/1e3)
-	default:
-		return fmt.Sprintf("%.0f bit/s", bitsPerSec)
+		return v.UI.Speed(0)
 	}
+	return v.UI.Speed(float64(bytesUploaded) / duration.Seconds())
 }
 
 // printSnapshotSummary prints the comprehensive snapshot completion summary
@@ -342,7 +332,7 @@ func (v *Vaultik) printSnapshotSummary(snapshotID string, startTime time.Time, s
 	}
 
 	v.UI.Complete("Created snapshot %s.", v.UI.Snapshot(snapshotID))
-	filesMsg := fmt.Sprintf("Files: %s examined, %s processed, %s unchanged",
+	filesMsg := fmt.Sprintf("Files: %s examined, %s backed up, %s unchanged",
 		v.UI.Count(stats.totalFiles),
 		v.UI.Count(totalFilesChanged),
 		v.UI.Count(stats.totalFilesSkipped))
@@ -351,7 +341,7 @@ func (v *Vaultik) printSnapshotSummary(snapshotID string, startTime time.Time, s
 	}
 	v.UI.Detail("%s.", filesMsg)
 
-	dataMsg := fmt.Sprintf("Data: %s total (%s processed)",
+	dataMsg := fmt.Sprintf("Data: %s total (%s backed up)",
 		v.UI.Size(totalBytesAll),
 		v.UI.Size(stats.totalBytes))
 	if stats.totalBytesDeleted > 0 {
@@ -368,7 +358,7 @@ func (v *Vaultik) printSnapshotSummary(snapshotID string, startTime time.Time, s
 			stats.totalBlobsUploaded,
 			v.UI.Size(stats.totalBytesUploaded),
 			v.UI.Duration(stats.uploadDuration),
-			formatUploadSpeed(stats.totalBytesUploaded, stats.uploadDuration))
+			v.uploadSpeed(stats.totalBytesUploaded, stats.uploadDuration))
 	}
 	v.UI.Detail("Snapshot create duration: %s.", v.UI.Duration(snapshotDuration))
 }