feat(subagent): 实验功能设置新增子代理模型配置

- 子代理设置页支持选择次主力模型，仅保存模型引用（不再写补丁字段），
  子代理直接继承所选模型的上下文长度与思考模式
- 界面只读展示继承的上下文长度与思考模式，移除补丁编辑项
- 仪表盘统计识别子代理请求（__secondary__）：归为「子代理模型（估算）」
  并缓存次主力模型定价；自定义网关模型价格按官方同名模型跨 provider 匹配
- bump v0.7.1

src/components/ui/controls.tsx

@@ -0,0 +1,104 @@
+import type { ReactNode } from "react";
+
+/** Shared small form controls used by settings panels (Agent settings,
+ *  Subagent settings, ...). Extracted from AgentSettingsPanel.tsx so new
+ *  panels can reuse the same look without duplicating code. */
+
+export function Card({ title, children }: { title: string; children: ReactNode }) {
+  return (
+    <div className="bg-panel border border-border rounded-xl p-4 space-y-3">
+      <h4 className="text-content-muted text-sm font-medium">{title}</h4>
+      {children}
+    </div>
+  );
+}
+
+export function Checkbox({
+  label,
+  checked,
+  disabled,
+  onChange,
+}: {
+  label: string;
+  checked: boolean;
+  disabled?: boolean;
+  onChange: (checked: boolean) => void;
+}) {
+  return (
+    <label
+      className={`flex items-center gap-2 text-sm ${
+        disabled ? "text-content-muted" : "text-content-primary"
+      }`}
+    >
+      <input
+        type="checkbox"
+        checked={checked}
+        disabled={disabled}
+        onChange={(e) => onChange(e.target.checked)}
+        className="rounded border-border bg-input text-blue-600 focus:ring-blue-500"
+      />
+      {label}
+    </label>
+  );
+}
+
+export function NumberField({
+  label,
+  value,
+  onChange,
+}: {
+  label: string;
+  value?: number;
+  onChange: (value: number | undefined) => void;
+}) {
+  return (
+    <label className="flex items-center gap-3 text-sm text-content-primary">
+      <span className="text-content-muted">{label}</span>
+      <input
+        type="number"
+        value={value ?? ""}
+        onChange={(e) => {
+          const raw = e.target.value;
+          onChange(raw === "" ? undefined : Number(raw));
+        }}
+        className="w-32 bg-input border border-border rounded px-2 py-1 text-sm focus:ring-2 focus:ring-blue-500 focus:outline-none"
+      />
+    </label>
+  );
+}
+
+export function Segmented({
+  options,
+  value,
+  onChange,
+  disabled,
+}: {
+  options: { key: string; label: string }[];
+  value: string;
+  onChange: (value: string) => void;
+  disabled?: boolean;
+}) {
+  return (
+    <div
+      className={`flex items-center rounded overflow-hidden border border-border ${
+        disabled ? "opacity-50" : ""
+      }`}
+    >
+      {options.map((opt) => (
+        <button
+          key={opt.key}
+          type="button"
+          disabled={disabled}
+          onClick={() => onChange(opt.key)}
+          className={`px-3 py-1 text-sm ${
+            value === opt.key
+              ? "bg-blue-600 text-white"
+              : "bg-input text-content-muted hover:bg-hover-2"
+          }`}
+        >
+          {opt.label}
+        </button>
+      ))}
+    </div>
+  );
+}