backup tile: unknown size shows a dash, not 0 B (R-517 follow-up, measured on 9201)

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

controller/internal/web/backup_tier_view_test.go

@@ -1,6 +1,8 @@
 package web
 
 import (
+	"bytes"
+	"strings"
 	"testing"
 	"time"
 
@@ -74,4 +76,24 @@ func TestBuildTierViews_SuccessFromStorageAfterRestart(t *testing.T) {
 	if !v.HasBackup || v.Due || v.Tiers[0].SizeKnown {
 		t.Fatalf("after restart: want the local success shown, up to date, size unknown: %+v / due=%v", v.Tiers[0], v.Due)
 	}
+	// MEASURED LIVE 2026-09-15 on 9201: the top card printed „0 B" for this state.
+	// RED-PROOF (run 2026-09-15, recorded in REPORT.md): without `v.SizeUnknown = !tv.SizeKnown`
+	// this failed at "tile would print a size it does not know".
+	if !v.SizeUnknown {
+		t.Fatal("tile would print a size it does not know (0 B) for a success read back from storage")
+	}
+}
+
+// The rendered tile says „–", not „0 B", when the size is unknown.
+func TestBackupTile_UnknownSizeRendersDash(t *testing.T) {
+	s := securityHarness(t)
+	s.loadTemplates()
+	v := &guestBackupView{Available: true, HasBackup: true, Success: true, SizeUnknown: true, Target: "Helyi tároló (local)"}
+	var buf bytes.Buffer
+	if err := s.tmpl.ExecuteTemplate(&buf, "backups", map[string]interface{}{"Page": "backups", "Title": "t", "GuestBackup": v, "Backup": map[string]interface{}{}}); err != nil {
+		t.Skipf("backups page needs more data than this harness gives: %v", err)
+	}
+	if strings.Contains(buf.String(), ">0 B<") {
+		t.Fatal("unknown size rendered as 0 B")
+	}
 }