Add admin token override feature for user accounts

- Add tokenOverride field to token usage bucket
- Create POST /api/admin/accounts/tokens endpoint for setting manual token limits
- Update admin accounts page to display token usage and override status
- Add 'Set Tokens' button to manually override user token limits for the month
- Override takes precedence over plan-based limits when set

chat/public/admin-accounts.html

@@ -78,6 +78,7 @@
                   <th style="padding:12px 8px;">Renews</th>
                   <th style="padding:12px 8px;">Created</th>
                   <th style="padding:12px 8px;">Last login</th>
+                  <th style="padding:12px 8px;">Tokens</th>
                   <th style="padding:12px 8px;">Actions</th>
                 </tr>
               </thead>