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/MapAnalyticsView.vue

@@ -5,6 +5,7 @@ import * as echarts from 'echarts'
 import type { ECharts } from 'echarts'
 import { useApi } from '@/composables/useApi'
 import type { MapAnalyticsSummary } from '@/types'
+import { safeFixed } from '@/utils/formatters'
 
 const api = useApi()
 
@@ -112,9 +113,9 @@ const downloadCSV = () => {
     m.map_name,
     m.seed ?? 'N/A',
     m.times_used,
-    m.avg_players.toFixed(1),
+    safeFixed(m.avg_players, 1),
     m.peak_players,
-    m.effectiveness_score.toFixed(1)
+    safeFixed(m.effectiveness_score, 1)
   ])
 
   const csv = [headers.join(','), ...rows.map(r => r.join(','))].join('\n')
@@ -183,7 +184,7 @@ onMounted(() => {
             {{ analytics.best_performing_map ?? 'No data' }}
           </p>
           <p class="text-xs text-neutral-600 mt-1" v-if="analytics.maps.length > 0">
-            Avg {{ analytics.maps[0]?.avg_players.toFixed(1) }} players
+            Avg {{ safeFixed(analytics?.maps?.[0]?.avg_players, 1) }} players
           </p>
         </div>
 
@@ -193,7 +194,7 @@ onMounted(() => {
             <p class="text-sm text-neutral-400">Rotation Effectiveness</p>
           </div>
           <p class="text-xl font-bold text-neutral-100">
-            {{ analytics.rotation_effectiveness.toFixed(1) }}%
+            {{ safeFixed(analytics?.rotation_effectiveness, 1) }}%
           </p>
           <p class="text-xs text-neutral-600 mt-1">Overall rotation health</p>
         </div>
@@ -245,7 +246,7 @@ onMounted(() => {
                 <td class="py-3 px-4 text-neutral-200 font-medium">{{ map.map_name }}</td>
                 <td class="py-3 px-4 text-neutral-400">{{ map.seed ?? '—' }}</td>
                 <td class="py-3 px-4 text-right text-neutral-300">{{ map.times_used }}</td>
-                <td class="py-3 px-4 text-right text-neutral-300">{{ map.avg_players.toFixed(1) }}</td>
+                <td class="py-3 px-4 text-right text-neutral-300">{{ safeFixed(map.avg_players, 1) }}</td>
                 <td class="py-3 px-4 text-right text-neutral-300">{{ map.peak_players }}</td>
                 <td class="py-3 px-4 text-right">
                   <span
@@ -256,7 +257,7 @@ onMounted(() => {
                       'bg-red-500/10 text-red-400': map.effectiveness_score < 60
                     }"
                   >
-                    {{ map.effectiveness_score.toFixed(1) }}%
+                    {{ safeFixed(map.effectiveness_score, 1) }}%
                   </span>
                 </td>
               </tr>