Print banner when vaultik is invoked with no subcommand

Cobra's default 'no subcommand → print help' path bypasses fx, so
the startup banner never ran for bare 'vaultik'. Add a Run handler
on the root command that prints the banner and then calls Help.

Extracted the banner-printing logic into writeStartupBanner() so
both this path and the fx setupGlobals hook share one implementation.

internal/cli/app.go

@@ -46,18 +46,25 @@ func setupGlobals(lc fx.Lifecycle, g *globals.Globals, v *vaultik.Vaultik, opts
 				// user-facing output is suppressed.
 				v.UI = ui.NewWithColor(io.Discard, false)
 			} else {
-				v.UI.Banner("%s %s by %s (commit %s, built on %s) starting up at %s.",
-					g.Appname, g.Version, globals.Author,
-					g.ShortCommit(), g.CommitDate,
-					g.StartTime.Format(time.RFC3339))
-				v.UI.Banner("%s", globals.Homepage)
-				v.UI.Banner("")
+				writeStartupBanner(v.UI, g.StartTime, g.ShortCommit())
 			}
 			return nil
 		},
 	})
 }
 
+// writeStartupBanner prints the two-line application banner followed by a
+// blank line. Used both from the fx hook (for subcommand invocations) and
+// from the root cobra Run handler (for `vaultik` with no subcommand).
+func writeStartupBanner(w *ui.Writer, startTime time.Time, shortCommit string) {
+	w.Banner("%s %s by %s (commit %s, built on %s) starting up at %s.",
+		globals.Appname, globals.Version, globals.Author,
+		shortCommit, globals.CommitDate,
+		startTime.Format(time.RFC3339))
+	w.Banner("%s", globals.Homepage)
+	w.Banner("")
+}
+
 // NewApp creates a new fx application with common modules.
 // It sets up the base modules (config, database, logging, globals) and
 // combines them with any additional modules specified in the options.

internal/cli/root.go

@@ -5,9 +5,12 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"time"
 
 	"github.com/adrg/xdg"
 	"github.com/spf13/cobra"
+	"sneak.berlin/go/vaultik/internal/globals"
+	"sneak.berlin/go/vaultik/internal/ui"
 )
 
 // RootFlags holds global flags that apply to all commands.
@@ -32,6 +35,18 @@ func NewRootCommand() *cobra.Command {
 public keys and uploads to S3-compatible storage. No private keys are needed
 on the source system.`,
 		SilenceUsage: true,
+		// When invoked with no subcommand, print the banner then the
+		// usage/help. Cobra's default behavior (without a Run) just
+		// prints help, which skips the banner.
+		Run: func(cmd *cobra.Command, args []string) {
+			startTime := time.Now().UTC()
+			short := globals.Commit
+			if len(short) > 12 {
+				short = short[:12]
+			}
+			writeStartupBanner(ui.New(os.Stdout), startTime, short)
+			_ = cmd.Help()
+		},
 	}
 
 	// Add global flags