fix(formatter): guard ShortenID/SmallSHA against short input

ShortenID and SmallSHA sliced their input to a fixed length without
checking it was long enough, panicking on shorter strings. Return the
input unchanged when it is already shorter than the cut. Also replace the
blank Commit placeholder with an explicit "unknown-commit" sentinel.

cmd/abra/main.go

@@ -16,7 +16,7 @@ func main() {
 		Version = "dev"
 	}
 	if Commit == "" {
-		Commit = "       "
+		Commit = "unknown-commit"
 	}
 
 	cli.Run(Version, Commit)

pkg/formatter/formatter.go

@@ -27,10 +27,16 @@ var BoldUnderlineStyle = lipgloss.NewStyle().
 	Underline(true)
 
 func ShortenID(str string) string {
+	if len(str) < 12 {
+		return str
+	}
 	return str[:12]
 }
 
 func SmallSHA(hash string) string {
+	if len(hash) < 8 {
+		return hash
+	}
 	return hash[:8]
 }