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/ui/detail_tab_test.go

@@ -0,0 +1,65 @@
+package ui
+
+import (
+	"testing"
+
+	"github.com/eslider/go-onlyoffice/cmd/office/model"
+)
+
+func TestDetailTabOrderProjectForm(t *testing.T) {
+	d := newDetailPane()
+	d.SetFocused(true)
+	d.LoadForm(model.Item{ID: "1", Kind: model.KindProject, Title: "P"}, model.FormFields{
+		PrimaryLabel: "Title", SecondaryLabel: "Description",
+		Primary: "Alpha", Secondary: "Beta", HasStatus: true,
+		Status: model.ProjectLifecycleOpen,
+	})
+
+	if d.tabStop != 0 || d.form.field != entityFieldPrimary {
+		t.Fatalf("start on title, tabStop=%d field=%d", d.tabStop, d.form.field)
+	}
+	if d.TabForward() {
+		t.Fatal("tab from title should stay in pane")
+	}
+	if d.form.field != entityFieldSecondary {
+		t.Fatalf("second stop should be description, field=%d", d.form.field)
+	}
+	if d.TabForward() {
+		t.Fatal("tab from description should stay in pane")
+	}
+	if d.form.field != entityFieldStatus {
+		t.Fatalf("third stop should be status, field=%d", d.form.field)
+	}
+	if d.TabForward() {
+		t.Fatal("tab from status should stay in pane")
+	}
+	if d.Zone() != detailZoneActions || d.actionIdx != 0 {
+		t.Fatalf("fourth stop should be Save, zone=%d idx=%d", d.Zone(), d.actionIdx)
+	}
+	if d.TabForward() {
+		t.Fatal("tab from Save should stay in pane")
+	}
+	if d.actionIdx != 1 {
+		t.Fatalf("fifth stop should be Delete, idx=%d", d.actionIdx)
+	}
+	if !d.TabForward() {
+		t.Fatal("tab from Delete should leave pane")
+	}
+	if d.tabStop != 0 {
+		t.Fatalf("after leaving pane tab order resets, tabStop=%d", d.tabStop)
+	}
+}
+
+func TestDetailShiftTabFromTitleLeavesPane(t *testing.T) {
+	d := newDetailPane()
+	d.SetFocused(true)
+	d.LoadForm(model.Item{ID: "1", Kind: model.KindProject}, model.FormFields{
+		PrimaryLabel: "Title", SecondaryLabel: "Description",
+	})
+	if !d.TabBackward() {
+		t.Fatal("shift+tab from title should leave pane")
+	}
+	if d.tabStop != d.maxTabStop() {
+		t.Fatalf("should park on last stop, tabStop=%d max=%d", d.tabStop, d.maxTabStop())
+	}
+}