feat(office): table detail panes and Alt+1/2/3 layout toggles

Add spreadsheet-style list, split detail pane with forms and document preview,
and Alt+1/2/3 to show/hide panes with even width distribution.

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

cmd/office/model/formfields_test.go

@@ -0,0 +1,20 @@
+package model
+
+import "testing"
+
+func TestFormFieldsFromRawMail(t *testing.T) {
+	raw := map[string]any{"subject": "Hi", "body": "Hello"}
+	f := FormFieldsFromRaw(KindMail, raw)
+	if f.Primary != "Hi" || f.Secondary != "Hello" || !f.ReadOnly {
+		t.Fatalf("unexpected mail fields: %+v", f)
+	}
+}
+
+func TestIsDocumentKind(t *testing.T) {
+	if !IsDocumentKind(KindFile) {
+		t.Fatal("file should be document")
+	}
+	if IsDocumentKind(KindTask) {
+		t.Fatal("task should be form")
+	}
+}