feat: 增加共享 Agent Browser 调试能力

需求：在 AI 编程会话中让用户与 Agent 共享同一浏览器页面，并查看控制台与网络信息。

实现：新增沙箱浏览器内核、Host API/渲染器面板、OpenCode 工具接入及安全边界测试。

electron/api/renderer-capability.ts

@@ -0,0 +1,21 @@
+import { randomBytes } from 'node:crypto';
+import type { IncomingMessage } from 'node:http';
+
+export const RENDERER_CAPABILITY_HEADER = 'x-niancode-renderer-capability';
+
+let rendererCapability = '';
+
+export function rotateRendererCapability(): void {
+  rendererCapability = randomBytes(32).toString('hex');
+}
+
+export function getRendererCapability(): string {
+  return rendererCapability;
+}
+
+export function hasRendererCapability(req: IncomingMessage): boolean {
+  const value = req.headers[RENDERER_CAPABILITY_HEADER];
+  return typeof value === 'string'
+    && rendererCapability.length > 0
+    && value === rendererCapability;
+}