refactor: add browser plugin runtime package

extensions/browser/runtime-api.ts

@@ -0,0 +1,10 @@
+export { createBrowserTool } from "./src/browser-tool.js";
+export { registerBrowserCli } from "./src/cli/browser-cli.js";
+export { createBrowserPluginService } from "./src/plugin-service.js";
+export { handleBrowserGatewayRequest } from "./src/gateway/browser-request.js";
+export {
+  definePluginEntry,
+  type OpenClawPluginApi,
+  type OpenClawPluginToolContext,
+  type OpenClawPluginToolFactory,
+} from "openclaw/plugin-sdk/plugin-entry";