refactor: normalize date handling to Tehran timezone

- Updated date handling in BlogSeoFields and ScheduleSection to use Tehran timezone utilities for consistency.
- Introduced `toTehranClockTime`, `tehranWallClockToUnix`, and `todayIso` functions for accurate date representation.
- Modified various components to utilize these new utilities, ensuring that date strings are correctly formatted and timestamps are accurately converted.
- Enhanced API documentation to clarify the handling of date fields, emphasizing the importance of server-local midnight.
- Added tests to verify that date overrides and holidays maintain the correct day without shifting due to timezone discrepancies.

assets/admin/lib/patientForm.test.ts

@@ -9,11 +9,16 @@ import type { PatientProfile } from '@/types';
 import type { PatientFormValues } from '@/components/PatientRecordInfoForm';
 
 describe('date helpers', () => {
-    it('timestamp ↔ YYYY-MM-DD رفت‌وبرگشت', () => {
+    // مبنا نیمه‌شبِ تهران است (نه UTC)، چون بک‌اند هم تاریخ‌های روزمحور را با
+    // strtotime در تایم‌زون سرور (Asia/Tehran) ذخیره می‌کند.
+    it('timestamp ↔ YYYY-MM-DD رفت‌وبرگشت روی نیمه‌شبِ تهران', () => {
         const ts = dateStrToTs('2025-01-07');
-        expect(ts).toBe(Math.floor(Date.parse('2025-01-07T00:00:00Z') / 1000));
+        expect(ts).toBe(Math.floor(Date.UTC(2025, 0, 6, 20, 30, 0) / 1000));
         expect(tsToDateStr(ts)).toBe('2025-01-07');
     });
+    it('timestampهای ساخته‌شده توسط سرور یک روز عقب نمی‌روند', () => {
+        expect(tsToDateStr(Math.floor(Date.UTC(2026, 6, 28, 20, 30, 0) / 1000))).toBe('2026-07-29');
+    });
     it('خالی/نامعتبر → مقدار تهی', () => {
         expect(tsToDateStr(null)).toBe('');
         expect(tsToDateStr(0)).toBe('');