Fix role change silently failing via @bind

The role <select> used a manual value=/@onchange pattern that parsed
e.Value and returned silently when the parse failed, so changing a role
did nothing and showed no message. Switch to @bind + @bind:after so the
framework handles the enum conversion, and log/verify the persisted role
in UpdateRoleAsync (now returns the previous role) for diagnosis.

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

Services/Auth/UserService.cs

@@ -1,5 +1,6 @@
 using System.Security.Claims;
 using Microsoft.AspNetCore.Identity;
+using Microsoft.Extensions.Logging;
 using SharepointToolbox.Web.Core.Models;
 using SharepointToolbox.Web.Infrastructure.Persistence;
 
@@ -9,11 +10,13 @@ public class UserService : IUserService
 {
     private readonly UserRepository _repo;
     private readonly IPasswordHasher<AppUser> _hasher;
+    private readonly ILogger<UserService> _logger;
 
-    public UserService(UserRepository repo, IPasswordHasher<AppUser> hasher)
+    public UserService(UserRepository repo, IPasswordHasher<AppUser> hasher, ILogger<UserService> logger)
     {
         _repo = repo;
         _hasher = hasher;
+        _logger = logger;
     }
 
     public async Task<AppUser> ProvisionAsync(ClaimsPrincipal principal)
@@ -56,13 +59,23 @@ public class UserService : IUserService
 
     public Task<IReadOnlyList<AppUser>> GetAllAsync() => _repo.LoadAsync();
 
-    public async Task UpdateRoleAsync(string userId, UserRole role)
+    public async Task<UserRole> UpdateRoleAsync(string userId, UserRole role)
     {
         var users = (await _repo.LoadAsync()).ToList();
         var user  = users.FirstOrDefault(u => u.Id == userId)
-                    ?? throw new KeyNotFoundException($"User {userId} not found.");
+                    ?? throw new KeyNotFoundException($"User '{userId}' not found among {users.Count} stored users.");
+
+        var oldRole = user.Role;
         user.Role = role;
         await _repo.UpsertAsync(user);
+
+        // Verify the write landed by re-reading the row from disk.
+        var persisted = (await _repo.LoadAsync()).FirstOrDefault(u => u.Id == user.Id)?.Role;
+        _logger.LogInformation(
+            "UpdateRoleAsync: {Email} (id {Id}) {OldRole} → {NewRole}; persisted value now {Persisted}.",
+            user.Email, user.Id, oldRole, role, persisted);
+
+        return oldRole;
     }
 
     public Task DeleteAsync(string userId) => _repo.DeleteAsync(userId);