fix(GRO-642): sanitize logo MIME type to prevent XSS in data URL rendering

Add ALLOWED_LOGO_TYPES allowlist check before constructing data URL from
user-controlled logoBase64 and logoMimeType fields. Only MIME types that
the API explicitly accepts (image/png, image/jpeg, image/gif, image/webp,
image/svg+xml) can be rendered as data URLs.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/src/pages/Settings.tsx

@@ -27,6 +27,8 @@ interface AuthProviderForm {
 
 const REDACTED = "••••••••";
 
+const ALLOWED_LOGO_TYPES = new Set(["image/png", "image/jpeg", "image/gif", "image/webp", "image/svg+xml"]);
+
 interface CurrentUser {
   id: string;
   name: string;
@@ -326,7 +328,7 @@ issuerUrl: authForm.issuerUrl,
 
   if (!loaded) return <p>Loading settings...</p>;
 
-  const logoSrc = form.logoUrl ?? (form.logoBase64 && form.logoMimeType ? `data:${form.logoMimeType};base64,${form.logoBase64}` : null);
+  const logoSrc = form.logoUrl ?? (form.logoBase64 && form.logoMimeType && ALLOWED_LOGO_TYPES.has(form.logoMimeType) ? `data:${form.logoMimeType};base64,${form.logoBase64}` : null);
 
   return (
     <div style={{ maxWidth: 600 }}>