Print banner before cobra parsing; route arg errors through ui.Error

Two output-style fixes plus a quiet-mode correction.

Banner: a manual scan of os.Args in CLIEntry decides whether to suppress
the banner (--quiet/-q/--cron), then prints it before cobra parses any
arguments. This makes the banner appear even when cobra rejects bad args
("requires at least 2 arg(s)") and on --help — paths that previously
skipped PersistentPreRun entirely. The cobra-side hook plumbing (sync.Once,
PersistentPreRun, custom HelpFunc) is removed.

Errors: rootCmd.SilenceErrors = true so cobra no longer prints its own
"Error: <msg>" line. Any error returned from Execute() goes through
ui.New(os.Stderr).Error(...), giving the documented "🛑 ERROR: <msg>"
format. A new helper cli.ReportError() formats errors from goroutine
paths that can't return through cobra's normal return chain; every
CLI command's fx-goroutine error path now calls it alongside the
existing structured log.Error so both channels record the failure.

Quiet mode: previously --quiet/--cron swapped Vaultik.UI to io.Discard,
which silenced Warning and Error messages too — contradicting the
documented "suppresses non-error output" semantics. ui.Writer now has
a SetQuiet flag that drops Begin/Complete/Info/Notice/Detail/Progress/
Banner only; Warning and Error always emit.

Also folds in restore.go cleanups the audit flagged: the hardcoded
"WARNING:" prefix on the failed-files block now uses ui.Warning +
ui.Detail, the post-restore "Restored N files" line uses ui.Complete,
and the "No files found to restore" branch emits both log.Warn and
ui.Warning so structured logs continue to capture it under --verbose.

internal/vaultik/integration_test.go

@@ -20,6 +20,7 @@ import (
 	"sneak.berlin/go/vaultik/internal/snapshot"
 	"sneak.berlin/go/vaultik/internal/storage"
 	"sneak.berlin/go/vaultik/internal/types"
+	"sneak.berlin/go/vaultik/internal/ui"
 	"sneak.berlin/go/vaultik/internal/vaultik"
 )
 
@@ -520,6 +521,7 @@ func TestBackupAndRestore(t *testing.T) {
 		Fs:      fs,
 		Stdout:  io.Discard,
 		Stderr:  io.Discard,
+		UI:      ui.NewWithColor(io.Discard, false),
 	}
 	vaultikApp.SetContext(ctx)
 
@@ -666,6 +668,7 @@ func TestEndToEndFileStorage(t *testing.T) {
 		Fs:      fs,
 		Stdout:  io.Discard,
 		Stderr:  io.Discard,
+		UI:      ui.NewWithColor(io.Discard, false),
 	}
 	restoreVaultik.SetContext(ctx)
 
@@ -803,6 +806,7 @@ func TestDedupOnlySnapshotRestores(t *testing.T) {
 		Fs:      fs,
 		Stdout:  io.Discard,
 		Stderr:  io.Discard,
+		UI:      ui.NewWithColor(io.Discard, false),
 	}
 	restoreVaultik.SetContext(ctx)
 

internal/vaultik/restore.go

@@ -93,10 +93,12 @@ func (v *Vaultik) Restore(opts *RestoreOptions) error {
 
 	if len(files) == 0 {
 		log.Warn("No files found to restore")
+		v.UI.Warning("No files found to restore.")
 		return nil
 	}
 
 	log.Info("Found files to restore", "count", len(files))
+	v.UI.Info("Found %s files to restore.", v.UI.Count(len(files)))
 
 	// Step 3: Create target directory
 	if err := v.Fs.MkdirAll(opts.TargetDir, 0755); err != nil {
@@ -125,16 +127,16 @@ func (v *Vaultik) Restore(opts *RestoreOptions) error {
 		"duration", result.Duration,
 	)
 
-	v.printfStdout("Restored %d files (%s) in %s\n",
-		result.FilesRestored,
-		humanize.Bytes(uint64(result.BytesRestored)),
-		result.Duration.Round(time.Second),
+	v.UI.Complete("Restored %s files (%s) in %s.",
+		v.UI.Count(result.FilesRestored),
+		v.UI.Size(result.BytesRestored),
+		v.UI.Duration(result.Duration),
 	)
 
 	if result.FilesFailed > 0 {
-		_, _ = fmt.Fprintf(v.Stdout, "\nWARNING: %d file(s) failed to restore:\n", result.FilesFailed)
+		v.UI.Warning("%d file(s) failed to restore:", result.FilesFailed)
 		for _, path := range result.FailedFiles {
-			_, _ = fmt.Fprintf(v.Stdout, "  - %s\n", path)
+			v.UI.Detail("%s", v.UI.Path(path))
 		}
 	}