feat(proxy): add rectifier config with master switch

- Add RectifierConfig struct with enabled and requestThinkingSignature fields
- Update should_rectify_thinking_signature to check master switch first
- Add tests for master switch functionality

src/components/settings/RectifierConfigPanel.tsx

@@ -0,0 +1,75 @@
+import { useEffect, useState } from "react";
+import { useTranslation } from "react-i18next";
+import { toast } from "sonner";
+import { Switch } from "@/components/ui/switch";
+import { Label } from "@/components/ui/label";
+import { settingsApi, type RectifierConfig } from "@/lib/api/settings";
+
+export function RectifierConfigPanel() {
+  const { t } = useTranslation();
+  const [config, setConfig] = useState<RectifierConfig>({
+    enabled: true,
+    requestThinkingSignature: true,
+  });
+  const [isLoading, setIsLoading] = useState(true);
+
+  useEffect(() => {
+    settingsApi
+      .getRectifierConfig()
+      .then(setConfig)
+      .catch((e) => console.error("Failed to load rectifier config:", e))
+      .finally(() => setIsLoading(false));
+  }, []);
+
+  const handleChange = async (updates: Partial<RectifierConfig>) => {
+    const newConfig = { ...config, ...updates };
+    setConfig(newConfig);
+    try {
+      await settingsApi.setRectifierConfig(newConfig);
+    } catch (e) {
+      console.error("Failed to save rectifier config:", e);
+      toast.error(String(e));
+      setConfig(config);
+    }
+  };
+
+  if (isLoading) return null;
+
+  return (
+    <div className="space-y-6">
+      <div className="flex items-center justify-between">
+        <div className="space-y-0.5">
+          <Label>{t("settings.advanced.rectifier.enabled")}</Label>
+          <p className="text-xs text-muted-foreground">
+            {t("settings.advanced.rectifier.enabledDescription")}
+          </p>
+        </div>
+        <Switch
+          checked={config.enabled}
+          onCheckedChange={(checked) => handleChange({ enabled: checked })}
+        />
+      </div>
+
+      <div className="space-y-4">
+        <h4 className="text-sm font-medium text-muted-foreground">
+          {t("settings.advanced.rectifier.requestGroup")}
+        </h4>
+        <div className="flex items-center justify-between pl-4">
+          <div className="space-y-0.5">
+            <Label>{t("settings.advanced.rectifier.thinkingSignature")}</Label>
+            <p className="text-xs text-muted-foreground">
+              {t("settings.advanced.rectifier.thinkingSignatureDescription")}
+            </p>
+          </div>
+          <Switch
+            checked={config.requestThinkingSignature}
+            disabled={!config.enabled}
+            onCheckedChange={(checked) =>
+              handleChange({ requestThinkingSignature: checked })
+            }
+          />
+        </div>
+      </div>
+    </div>
+  );
+}