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/Models/Auth/AuthDtos.cs

@@ -2,6 +2,9 @@ namespace Meezi.API.Models.Auth;
 
 public record SendOtpRequest(string Phone);
 
+/// <summary>Username + password login (alternative to OTP). Optional cafeId to scope to a specific café.</summary>
+public record LoginWithPasswordRequest(string Username, string Password, string? CafeId = null);
+
 public record VerifyOtpRequest(string Phone, string Code, string? CafeId = null);
 
 public record RefreshTokenRequest(string RefreshToken);

src/Meezi.API/Models/Hr/HrDtos.cs

@@ -59,3 +59,6 @@ public record CreateSalaryRequest(
     decimal Deductions);
 
 public record TodayShiftDto(ShiftType ShiftType, string Label);
+
+/// <summary>Set or update username/password credentials for an employee.</summary>
+public record SetEmployeeCredentialsRequest(string Username, string Password);