feat: username/password authentication for admin and merchant panels

- Add PasswordHasher utility (PBKDF2/SHA-256, 100k iterations)
- Add Username + PasswordHash fields to Employee and SystemAdmin entities
- EF migration: AddPasswordLogin (nullable columns on both tables)
- Meezi.API: POST /api/auth/login (employee password login, CHOOSE_CAFE support)
- Meezi.API: PUT/DELETE /api/cafes/{id}/employees/{id}/credentials (Owner/Manager only)
- Meezi.Admin.API: POST /api/admin/auth/login + PUT /api/admin/auth/password
- Dashboard login page: OTP / Password tabs
- Admin login page: OTP / Password tabs
- HR screen: new Credentials tab for setting employee username/password
- PlatformDataSeeder: ensure system admin + integration settings in production
- Trial countdown banner: updated deadline to 1 Tir 1405 (Jun 22)
- i18n: fa/en/ar updated for all new UI strings

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/Meezi.API/Services/IAuthService.cs

@@ -16,6 +16,10 @@ public interface IAuthService
         VerifyOtpRequest request,
         CancellationToken cancellationToken = default);
 
+    Task<(bool Success, AuthTokenResponse? Data, string? ErrorCode, string? ErrorMessage, CafeChoicesResponse? Choices)> LoginWithPasswordAsync(
+        LoginWithPasswordRequest request,
+        CancellationToken cancellationToken = default);
+
     Task<(bool Success, AuthTokenResponse? Data, string? ErrorCode, string? ErrorMessage)> SwitchCafeAsync(
         string employeeId, string targetCafeId,
         CancellationToken cancellationToken = default);