feat: port tauri create-service payment flow to admin session settlement

Port the tauri /files/create-service page (payment mode) to the admin SPA
and back it with real multi-part session settlement:

Backend:
- New SessionPayment entity (session_payments table): partial payments
  per session with method (wallet/pos/cash/card), amount, paid_at, actor
- PatientSession: settlement discount (percent/fixed), discount_rials,
  paid_at, payments relation; remaining debt derived from
  final - discount - paid total
- POST /api/v1/session/{uuid}/payments: register a partial payment;
  wallet method debits the patient wallet; zero remaining marks paid
- PATCH /api/v1/session/{uuid}: accepts discount_type/discount_value
  (null removes) and paid_at, backward compatible
- New error codes: ERR_SESSION_PAYMENT_INVALID/_EXCEEDS,
  ERR_SESSION_DISCOUNT_INVALID
- Migration + 14 functional tests (partial/full/wallet/exceed/discount)

Frontend (admin):
- SessionPaymentPage: two-step stepper (پرداخت ← جزییات) ported from
  tauri AddService payment mode — service cost, settlement discount
  input, Jalali payment date, wallet balance, 4-method payment accordion,
  paid-list box, details summary
- SessionStepper + stepper/payment icons ported verbatim from tauri SVGs
- «تکمیل پرداخت» on SessionServiceCard now navigates to the payment page
  (replaces the small settle modal on PatientDetailPage)
- Routes for patients/ and my-patients/ variants; vitest coverage
- docs/api/patient.md updated

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/Shared/Constant/ErrorCodes.php

@@ -62,6 +62,9 @@ class ErrorCodes
     // Patient
     public const ERR_PATIENT_NOT_FOUND  = 'ERR_PATIENT_NOT_FOUND';
     public const ERR_SESSION_NOT_FOUND  = 'ERR_SESSION_NOT_FOUND';
+    public const ERR_SESSION_PAYMENT_INVALID  = 'ERR_SESSION_PAYMENT_INVALID';
+    public const ERR_SESSION_PAYMENT_EXCEEDS  = 'ERR_SESSION_PAYMENT_EXCEEDS';
+    public const ERR_SESSION_DISCOUNT_INVALID = 'ERR_SESSION_DISCOUNT_INVALID';
 
     // Profile
     public const ERR_PROFILE_NATIONAL_CODE_TAKEN = 'ERR_PROFILE_001';
@@ -146,6 +149,9 @@ class ErrorCodes
             self::ERR_PROFILE_NATIONAL_CODE_TAKEN => 'این کد ملی قبلاً برای کاربر دیگری ثبت شده است',
             self::ERR_PROFILE_MOBILE_TAKEN        => 'این شماره موبایل قبلاً برای کاربر دیگری ثبت شده است',
             self::ERR_SESSION_NOT_FOUND      => 'مراجعه یافت نشد',
+            self::ERR_SESSION_PAYMENT_INVALID  => 'مبلغ یا روش پرداخت نامعتبر است',
+            self::ERR_SESSION_PAYMENT_EXCEEDS  => 'مبلغ پرداخت از مانده بدهی بیشتر است',
+            self::ERR_SESSION_DISCOUNT_INVALID => 'مقدار تخفیف نامعتبر است',
             self::ERR_SMS_WALLET_INSUFFICIENT => 'موجودی کیف پیامک کافی نیست',
             self::ERR_WALLET_INSUFFICIENT    => 'موجودی کیف پول کافی نیست',
             self::ERR_RATING_NOT_ELIGIBLE    => 'برای ثبت نظر یا امتیاز باید در یک ماه گذشته نوبت تایید‌شده نزد این پزشک داشته باشید',