fix(server): hide CLOSED rows from preview for legacy mini-program compatibility

The previous fix made publishDaySlots CLOSE rows instead of DELETE them.
That works correctly on the server, but the live mini-program still ships
the old schedule.vue which only knows about isPublished (no status
field). It would re-render the CLOSED rows with the '已发布' badge,
making it look like 'clear day' did nothing.

Hide CLOSED rows from getSchedulePreview so the legacy client shows
'当日暂无排课' for rest days — the same UX it had before this fix
shipped. All-CLOSED days return []; days with a mix return only the
non-CLOSED rows; days the cron hasn't touched still return the ghost
template.

The republished mini-program (with status-aware rendering) will see the
same [] for rest days, which is consistent. Tests: 4 new specs covering
all-OPEN / all-CLOSED / mixed / empty-day cases.

packages/server/src/time-slot/__tests__/time-slot.service.spec.ts

@@ -231,6 +231,69 @@ describe('TimeSlotService', () => {
     })
   })
 
+  // -------------------------------------------------------------------------
+  // getSchedulePreview
+  // -------------------------------------------------------------------------
+  describe('getSchedulePreview', () => {
+    const date = '2026-04-07'
+
+    it('returns OPEN/FULL rows with isPublished: true', async () => {
+      mockPrisma.timeSlot.findMany.mockResolvedValueOnce([
+        makeSlot({ id: 'slot-1', startTime: '09:00', endTime: '10:00', status: TimeSlotStatus.OPEN }),
+        makeSlot({ id: 'slot-2', startTime: '10:30', endTime: '11:30', status: TimeSlotStatus.FULL }),
+      ])
+
+      const result = await service.getSchedulePreview(date)
+
+      expect(result).toHaveLength(2)
+      expect(result.every((s) => s.isPublished === true)).toBe(true)
+    })
+
+    it('HIDES CLOSED rows so the legacy client does not render them as "已发布"', async () => {
+      // Simulates an admin "clear day" — DB now has 13 CLOSED rows.
+      mockPrisma.timeSlot.findMany.mockResolvedValueOnce(
+        Array.from({ length: 13 }, (_, i) =>
+          makeSlot({
+            id: `slot-${i}`,
+            startTime: `${String(8 + Math.floor(i / 2)).padStart(2, '0')}:${i % 2 === 0 ? '00' : '30'}`,
+            endTime: `${String(8 + Math.floor(i / 2)).padStart(2, '0')}:${i % 2 === 0 ? '30' : '30'}`,
+            status: TimeSlotStatus.CLOSED,
+          }),
+        ),
+      )
+
+      const result = await service.getSchedulePreview(date)
+
+      // Critical for online compatibility: the legacy client must see []
+      // so it shows "当日暂无排课", not 13 phantom "已发布" slots.
+      expect(result).toEqual([])
+    })
+
+    it('returns the OPEN subset and hides CLOSED when mixed', async () => {
+      mockPrisma.timeSlot.findMany.mockResolvedValueOnce([
+        makeSlot({ id: 'open-1', status: TimeSlotStatus.OPEN }),
+        makeSlot({ id: 'closed-1', status: TimeSlotStatus.CLOSED, startTime: '10:00', endTime: '11:00' }),
+        makeSlot({ id: 'open-2', status: TimeSlotStatus.OPEN, startTime: '10:30', endTime: '11:30' }),
+      ])
+
+      const result = await service.getSchedulePreview(date)
+
+      expect(result).toHaveLength(2)
+      expect(result.map((s) => s.id).sort()).toEqual(['open-1', 'open-2'])
+      expect(result.find((s) => s.id === 'closed-1')).toBeUndefined()
+    })
+
+    it('returns the ghost template when the day has no rows at all', async () => {
+      mockPrisma.timeSlot.findMany.mockResolvedValueOnce([])
+
+      const result = await service.getSchedulePreview(date)
+
+      // Ghost = isPublished false, id null.
+      expect(result.length).toBeGreaterThan(0)
+      expect(result.every((s) => s.isPublished === false && s.id === null)).toBe(true)
+    })
+  })
+
   // -------------------------------------------------------------------------
   // createManualSlot
   // -------------------------------------------------------------------------