Add OTP login flow and multi-cafe role switching

Introduce an OTP input box on login/register, surface user roles and a
cafe chooser, add a dashboard switch button in the POS screen, and
register OTP validators explicitly to survive Docker layer caching.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/Meezi.Admin.API/Extensions/AdminServiceCollectionExtensions.cs

@@ -5,6 +5,7 @@ using Microsoft.AspNetCore.Authentication.JwtBearer;
 using Microsoft.IdentityModel.Tokens;
 using Meezi.Admin.API.Hubs;
 using Meezi.Admin.API.Services;
+using Meezi.Admin.API.Models;
 using Meezi.Admin.API.Validators;
 using Meezi.Infrastructure;
 using Serilog;
@@ -38,6 +39,10 @@ public static class AdminServiceCollectionExtensions
         services.AddSwaggerGen();
         services.AddSignalR();
         services.AddValidatorsFromAssemblyContaining<SendOtpRequestValidator>();
+        // Explicit registrations as safety net (assembly scan can miss in some Docker layer caches)
+        services.AddScoped<IValidator<SendOtpRequest>, SendOtpRequestValidator>();
+        services.AddScoped<IValidator<VerifyOtpRequest>, VerifyOtpRequestValidator>();
+        services.AddScoped<IValidator<RefreshTokenRequest>, RefreshTokenRequestValidator>();
 
         var jwtKey = configuration["Jwt:Key"] ?? "meezi-dev-secret-key-min-32-chars!!";
         var jwtIssuer = configuration["Jwt:Issuer"] ?? "meezi";