fix: update AAD display name to Microsoft Entra ID in auth UI

Updates the auth emulator UI to show "Microsoft Entra ID" instead of "AAD"
while maintaining backward compatibility by keeping 'aad' as the underlying
provider value. Also adds clarification in help text.

Fixes #850

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: keith-oak

src/public/auth.html

@@ -78,15 +78,15 @@ <h1 class="pb-4">Azure Static Web Apps Auth</h1>
                     required="required"
                     class="form-control"
                   />
-                  <small id="identityProviderHelpBlock" class="form-text text-muted">Name of the identity provider</small>
+                  <small id="identityProviderHelpBlock" class="form-text text-muted">Name of the identity provider (aad = Microsoft Entra ID)</small>
                 </div>
                 <datalist id="providers-list">
-                  <option value="aad"></option>
-                  <option value="google"></option>
-                  <option value="github"></option>
-                  <option value="twitter"></option>
-                  <option value="facebook"></option>
-                  <option value="openid"></option>
+                  <option value="aad">Microsoft Entra ID</option>
+                  <option value="google">Google</option>
+                  <option value="github">GitHub</option>
+                  <option value="twitter">Twitter</option>
+                  <option value="facebook">Facebook</option>
+                  <option value="openid">OpenID</option>
                 </datalist>
               </div>