feat(office): mail preview, infinite scroll, pane resize, and scrollbars

Polish the office TUI with proportional pane layout, drag resize, live
filtering, HTML mail preview, paginated mail lists, overflow scrollbars,
flattened navigation, and project save/status fixes; add UpdateProjectStatus.

Co-authored-by: Cursor <cursoragent@cursor.com>

cmd/office/fetch/save_integration_test.go

@@ -0,0 +1,52 @@
+//go:build integration
+
+package fetch_test
+
+import (
+	"testing"
+	"time"
+
+	"github.com/eslider/go-onlyoffice/cmd/office/model"
+)
+
+func TestIntegrationSaveProject(t *testing.T) {
+	loader, ctx := liveLoader(t)
+	items, err := loader.List(ctx, model.ListSpec{Subject: model.SubjectProjects})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(items) == 0 {
+		t.Skip("no projects")
+	}
+	item := items[0]
+	fields, err := loader.DetailForm(ctx, item)
+	if err != nil {
+		t.Fatalf("DetailForm: %v", err)
+	}
+	if fields.ResponsibleID == "" {
+		t.Skip("project has no responsible id on this instance")
+	}
+	marker := " office-save-test " + time.Now().UTC().Format(time.RFC3339)
+	fields.Primary = fields.Primary + marker
+	if err := loader.SaveItem(ctx, item, fields); err != nil {
+		t.Fatalf("SaveItem: %v", err)
+	}
+	after, err := loader.DetailForm(ctx, item)
+	if err != nil {
+		t.Fatalf("DetailForm after save: %v", err)
+	}
+	if after.Primary != fields.Primary {
+		t.Fatalf("title not saved: got %q want %q", after.Primary, fields.Primary)
+	}
+	fields.Primary = stringsTrimSuffixMarker(after.Primary, marker)
+	if err := loader.SaveItem(ctx, item, fields); err != nil {
+		t.Logf("cleanup save: %v", err)
+	}
+}
+
+func stringsTrimSuffixMarker(s, marker string) string {
+	if len(s) >= len(marker) && s[len(s)-len(marker):] == marker {
+		return s[:len(s)-len(marker)]
+	}
+	return s
+}