fix(web): show ai route fallback evidence

apps/web/messages/en.json

@@ -253,7 +253,19 @@
       "humanGap": "Human gap",
       "humanGapDetail": "{gate} missing {count}",
       "modelRoute": "Model route",
-      "routeDetail": "{model}; fallback {fallback}",
+      "routeDetail": "{model}; current {selected}; {primary}={primaryStatus}; fallback {fallback}",
+      "routeReasonSeparator": "; ",
+      "routeReason": "Reason: {reason}",
+      "routeErrorDetail": "Route check failed: {error}",
+      "routeNoFallback": "none",
+      "routeHealth": {
+        "healthy": "healthy",
+        "slow": "slow",
+        "degraded": "degraded",
+        "offline": "offline",
+        "not_checked": "standby",
+        "unknown": "unknown"
+      },
       "topGap": "Largest current gap: {gate}, {count} items."
     }
   },

apps/web/messages/zh-TW.json

@@ -254,7 +254,19 @@
       "humanGap": "人工缺口",
       "humanGapDetail": "{gate} 缺 {count} 筆",
       "modelRoute": "模型路由",
-      "routeDetail": "{model}；備援 {fallback}",
+      "routeDetail": "{model}；目前 {selected}；{primary}={primaryStatus}；備援 {fallback}",
+      "routeReasonSeparator": "；",
+      "routeReason": "原因：{reason}",
+      "routeErrorDetail": "路由檢查失敗：{error}",
+      "routeNoFallback": "無",
+      "routeHealth": {
+        "healthy": "健康",
+        "slow": "偏慢",
+        "degraded": "降級",
+        "offline": "離線",
+        "not_checked": "待命",
+        "unknown": "未知"
+      },
       "topGap": "目前最大缺口：{gate}，共 {count} 筆。"
     }
   },