fix: harden countdown validation and recurrence

frontend/src/CountdownPanel.test.ts

@@ -52,6 +52,22 @@ describe('countdown modal accessibility', () => {
     expect(source).not.toContain("Promise.all([request('/countdowns'),request('/countdowns?archived=true')])")
   })
 
+  it('prevents duplicate submits and sends the edit precondition', () => {
+    expect(source).toContain('if (busy.value) return')
+    expect(source).toContain('payload.expected_updated_at=editingItem.value?.updated_at')
+    expect(source).toContain(':disabled="busy"')
+  })
+
+  it('keeps weekly and monthly recurrence available for lunar dates', () => {
+    expect(source).toContain('<option value="weekly">每周</option>')
+    expect(source).toContain('<option value="monthly">每月</option>')
+  })
+
+  it('does not repeat the lunar label in the converted date line', () => {
+    expect(source).toContain("return `${formatDate(item.display_date)}${suffix}`")
+    expect(source).not.toContain("`${formatDate(item.display_date)} · ${item.lunar_text}${suffix}`")
+  })
+
   it('keeps the empty state directly actionable', () => {
     expect(source).toContain('添加第一个重要日子')
     expect(source).toContain('@click="openFromEmpty"')