Group users by company + allow admins to set user/admin role

- Superadmin sees users grouped by company with header rows
- Admins can now set user or admin role when creating/editing users
- Admin role change restricted to own company only
- Prevents admin from modifying superadmin roles

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

index.html

@@ -2133,6 +2133,13 @@
                         <label>Yritykset ja roolit</label>
                         <div id="user-company-checkboxes" style="display:flex;flex-direction:column;gap:0.5rem;margin-top:0.25rem;"></div>
                     </div>
+                    <div class="form-group" id="admin-company-role-section" style="display:none;">
+                        <label>Rooli yrityksessä</label>
+                        <select id="admin-company-role-select" style="padding:6px 10px;border:2px solid #e0e0e0;border-radius:8px;font-size:0.85rem;">
+                            <option value="user">Käyttäjä</option>
+                            <option value="admin">Admin</option>
+                        </select>
+                    </div>
                 </div>
                 <div id="user-signatures-section" style="display:none;margin-top:1rem;border-top:1px solid #e5e7eb;padding-top:1rem;">
                     <h3 style="color:#0f3460;font-size:1rem;margin-bottom:0.75rem;">Sähköpostiallekirjoitukset</h3>