feat(api): expose cache metrics in REPL + normalize across providers (#813)

* feat(api): expose cache metrics in REPL + /cache-stats command

* fix(api): normalize Kimi/DeepSeek/Gemini cache fields through shim layer

* test(api): cover /cache-stats rendering + fix CacheMetrics docstring drift

* fix(api): always reset cache turn counter + include date in /cache-stats rows

* refactor(api): unify shim usage builder + add cost-tracker wiring test

* fix(api): classify private-IP/self-hosted OpenAI endpoints as N/A instead of cold

* fix(api): require colon guard on IPv6 ULA prefix to avoid public-host over-match

* perf(api): ring buffer for cache history + hit rate clamp + .localhost TLD

* fix(api): null guards on formatters + document Codex Responses API shape

* fix(api): defensive start-of-turn reset + config gate fallback + env var docs

* fix(api): trust forwarded cache data on self-hosted URLs (data-driven)

* refactor(api): delegate streaming Responses usage to shared makeUsage helper

src/components/Settings/Config.tsx

@@ -299,6 +299,26 @@ export function Config({
         enabled: toolHistoryCompressionEnabled
       });
     }
+  }, {
+    id: 'showCacheStats',
+    label: 'Cache stats display',
+    value: globalConfig.showCacheStats,
+    options: ['off', 'compact', 'full'],
+    type: 'enum' as const,
+    onChange(mode: string) {
+      const showCacheStats = (mode === 'off' || mode === 'compact' || mode === 'full' ? mode : 'compact') as 'off' | 'compact' | 'full';
+      saveGlobalConfig(current_cs => ({
+        ...current_cs,
+        showCacheStats
+      }));
+      setGlobalConfig({
+        ...getGlobalConfig(),
+        showCacheStats
+      });
+      logEvent('tengu_show_cache_stats_setting_changed', {
+        mode: showCacheStats as AnalyticsMetadata_I_VERIFIED_THIS_IS_NOT_CODE_OR_FILEPATHS
+      });
+    }
   }, {
     id: 'spinnerTipsEnabled',
     label: 'Show tips',