fix(failover): patch P1-P3 reliability gaps surfaced by team review

- Forwarder buffers non-streaming bodies and primes streaming first
  chunk before signaling success, so body timeouts and SSE first-chunk
  failures route through the circuit breaker instead of being recorded
  as success on response-header arrival
- Atomic enable-failover: switch to P1 before persisting the flag, and
  roll back auto-added queue entries when the switch is rejected
  (e.g. official providers)
- Hot-reload circuit breaker config on per-app proxy config change
  instead of waiting for a proxy restart
- FailoverToggle / FailoverQueueManager / AutoFailoverConfigPanel
  require proxy takeover for the active app; the backend command also
  rejects enabling when takeover is off
- ProviderHealthBadge consumes the backend is_healthy flag instead of
  hardcoding the 5-failure threshold

Cleanup:
- impl From<&AppProxyConfig> for CircuitBreakerConfig and use it from
  the command layer
- Collapse three identical TabsContent blocks into a single map

src/components/proxy/FailoverToggle.tsx

@@ -10,6 +10,7 @@ import {
   useAutoFailoverEnabled,
   useSetAutoFailoverEnabled,
 } from "@/lib/query/failover";
+import { useProxyStatus } from "@/hooks/useProxyStatus";
 import { cn } from "@/lib/utils";
 import { useTranslation } from "react-i18next";
 import type { AppId } from "@/lib/api";
@@ -24,8 +25,11 @@ export function FailoverToggle({ className, activeApp }: FailoverToggleProps) {
   const { data: isEnabled = false, isLoading } =
     useAutoFailoverEnabled(activeApp);
   const setEnabled = useSetAutoFailoverEnabled();
+  const { takeoverStatus } = useProxyStatus();
+  const takeoverEnabled = takeoverStatus?.[activeApp] ?? false;
 
   const handleToggle = (checked: boolean) => {
+    if (checked && !takeoverEnabled) return;
     setEnabled.mutate({ appType: activeApp, enabled: checked });
   };
 
@@ -36,15 +40,20 @@ export function FailoverToggle({ className, activeApp }: FailoverToggleProps) {
         ? "Codex"
         : "Gemini";
 
-  const tooltipText = isEnabled
-    ? t("failover.tooltip.enabled", {
+  const tooltipText = !takeoverEnabled
+    ? t("failover.tooltip.takeoverRequired", {
         app: appLabel,
-        defaultValue: `${appLabel} 故障转移已启用\n按队列优先级（P1→P2→...）选择供应商`,
+        defaultValue: `请先接管 ${appLabel}，再启用故障转移`,
       })
-    : t("failover.tooltip.disabled", {
-        app: appLabel,
-        defaultValue: `启用 ${appLabel} 故障转移\n将立即切换到队列 P1，并在失败时自动切换到下一个`,
-      });
+    : isEnabled
+      ? t("failover.tooltip.enabled", {
+          app: appLabel,
+          defaultValue: `${appLabel} 故障转移已启用\n按队列优先级（P1→P2→...）选择供应商`,
+        })
+      : t("failover.tooltip.disabled", {
+          app: appLabel,
+          defaultValue: `启用 ${appLabel} 故障转移\n将立即切换到队列 P1，并在失败时自动切换到下一个`,
+        });
 
   return (
     <div
@@ -69,7 +78,7 @@ export function FailoverToggle({ className, activeApp }: FailoverToggleProps) {
       <Switch
         checked={isEnabled}
         onCheckedChange={handleToggle}
-        disabled={setEnabled.isPending || isLoading}
+        disabled={setEnabled.isPending || isLoading || !takeoverEnabled}
       />
     </div>
   );

src/components/proxy/ProxyPanel.tsx

@@ -725,6 +725,7 @@ function ProviderQueueItem({
       {/* 健康徽章 */}
       <ProviderHealthBadge
         consecutiveFailures={health?.consecutive_failures ?? 0}
+        isHealthy={health?.is_healthy}
       />
     </div>
   );