fix(bi): use correct auth token key for cost-config API calls

Fixed authentication issue where loadCostConfig() and saveCostConfig()
were using wrong localStorage key 'tractatus_token' instead of
'admin_token' (accessed via getAuthToken()).

This caused "jwt malformed" 401 errors because:
- audit-logs endpoint: uses admin_token (works ✓)
- cost-config endpoint: was using tractatus_token (broken ✗)

Changed both functions to use getAuthToken() for consistency.

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

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

public/js/admin/audit-analytics.js

@@ -903,7 +903,7 @@ function showError(message) {
 // Cost Configuration
 async function loadCostConfig() {
   try {
-    const token = localStorage.getItem('tractatus_token');
+    const token = getAuthToken();
     const response = await fetch('/api/admin/cost-config', {
       headers: { 'Authorization': `Bearer ${token}` }
     });
@@ -922,7 +922,7 @@ async function loadCostConfig() {
 
 async function saveCostConfig(costFactors) {
   try {
-    const token = localStorage.getItem('tractatus_token');
+    const token = getAuthToken();
     const response = await fetch('/api/admin/cost-config', {
       method: 'POST',
       headers: {