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/AnalyticsView.vue

@@ -5,6 +5,7 @@ import * as echarts from 'echarts'
 import type { ECharts } from 'echarts'
 import { useApi } from '@/composables/useApi'
 import type { AnalyticsSummary, TimeseriesData } from '@/types'
+import { safeFixed } from '@/utils/formatters'
 
 const api = useApi()
 
@@ -268,7 +269,7 @@ onMounted(() => {
             <TrendingUp class="w-4 h-4 text-neutral-500" />
             <p class="text-sm text-neutral-400">Avg Players</p>
           </div>
-          <p class="text-2xl font-bold text-neutral-100">{{ summary.avg_players.toFixed(1) }}</p>
+          <p class="text-2xl font-bold text-neutral-100">{{ safeFixed(summary?.avg_players, 1) }}</p>
           <p class="text-xs text-neutral-600 mt-1">Last {{ timeRange }}</p>
         </div>
         <div class="bg-neutral-900 border border-neutral-800 rounded-lg p-5">
@@ -276,7 +277,7 @@ onMounted(() => {
             <Clock class="w-4 h-4 text-neutral-500" />
             <p class="text-sm text-neutral-400">Uptime</p>
           </div>
-          <p class="text-2xl font-bold text-neutral-100">{{ summary.uptime_percentage.toFixed(1) }}%</p>
+          <p class="text-2xl font-bold text-neutral-100">{{ safeFixed(summary?.uptime_percentage, 1) }}%</p>
           <p class="text-xs text-neutral-600 mt-1">Last {{ timeRange }}</p>
         </div>
         <div class="bg-neutral-900 border border-neutral-800 rounded-lg p-5">