fix(profile): hide auth-error and main-content divs by default

Add hidden class to both #auth-error and #main-content so they only
show when JS explicitly displays them.

static/profile.html

@@ -31,14 +31,14 @@
 
 <div class="profile-container">
   <div id="loading"><i class="fas fa-circle-notch"></i> Loading…</div>
-  <div id="auth-error">
+  <div id="auth-error" class="hidden">
     <div class="err-icon"><i class="fas fa-lock"></i></div>
     <h2>Not Authenticated</h2>
     <p>Please sign in to view your profile.</p>
     <a href="/login"><i class="fas fa-sign-in-alt"></i> Sign in</a>
   </div>
 
-  <div id="main-content">
+  <div id="main-content" class="hidden">
     <div class="profile-card">
       <div class="avatar-section">
         <div class="avatar-large" id="p-avatar">—</div>