Pin the extension roadmap and downstream spike

Why: Downstream products need a published extension surface, contract checks, and a sample plugin that does not modify the base.
Evidence: scripts/lint-boundaries.sh printed boundaries ok. examples/downstream-rdm go test passed. Submodule pointers record the core, documents, backend, ui, and frontend commits for this roadmap.
Impact: make test runs the boundary lint first. make plugin-new scaffolds a declaration plugin. Version tags and remote downstream repositories are not created.
Refs: .task/feature-base-extension-roadmap.md
Co-authored-by: Cursor <cursoragent@cursor.com>

Makefile

@@ -96,7 +96,14 @@ test-ui: contracts
 test-agentcmd:
 	cd deps/agent-command && go vet ./... && go test -count=1 ./...
 
-test: test-core test-backend test-frontend test-ui test-agentcmd
+test-boundaries:
+	bash scripts/lint-boundaries.sh
+
+plugin-new:
+	@test -n "$(NAME)" || (echo "用法：make plugin-new NAME=<id>"; exit 2)
+	bash scripts/plugin-new.sh "$(NAME)"
+
+test: test-boundaries test-core test-backend test-frontend test-ui test-agentcmd
 
 # 运行演示（mock 模式）：单二进制 + 示例插件 + 嵌入式存储，浏览器 http://127.0.0.1:8787
 # 环境服务管理（scripts/svc.sh）：deploy = 停旧 → 构建 → 启动；dev/prod 相互隔离。