fix: Replace unsafe .toFixed() calls with safeFixed() in analytics views

- AnalyticsView: avg_players, uptime_percentage
- WipeAnalyticsView: success_rate, population curve, durations, CSV export
- PlayerRetentionView: retention percentages, session duration, tooltip
- MapAnalyticsView: rotation effectiveness, performance metrics, table

All analytics views now use safe formatter utilities with optional chaining
to prevent null/undefined runtime errors when displaying numeric data.

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

frontend/src/views/admin/StoreItemsView.vue

@@ -3,6 +3,7 @@ import { ref, computed, onMounted } from 'vue'
 import { useApi } from '@/composables/useApi'
 import type { StoreCategory, StoreItem } from '@/types'
 import { ShoppingBag, Plus, Trash2, RefreshCw, Edit2, DollarSign, X } from 'lucide-vue-next'
+import { safeFixed } from '@/utils/formatters'
 
 const api = useApi()
 
@@ -405,7 +406,7 @@ onMounted(() => {
             <td class="px-4 py-3">
               <div class="flex items-center gap-1 text-sm text-neutral-200">
                 <DollarSign class="w-3.5 h-3.5 text-neutral-500" />
-                {{ item.price.toFixed(2) }}
+                {{ safeFixed(item.price, 2) }}
               </div>
             </td>
             <td class="px-4 py-3 text-sm text-neutral-400 font-mono">