feat(prompts): v2 DB 控制面热切换 —— 版本留存 + 不重启即生效

在 v1(注册表+文件覆盖)上加 DB 管理层与热切换，镜像 model-config 控制面：
- store: sundynix_prompt 表(key/version/content/active) + ActivePrompts/ListPrompts/
  CreateVersion/Activate/Deactivate
- 控制面: ServePrompts/RequestActivePrompts(+Retry)/PublishPromptsUpdated/SubscribePromptsUpdated；
  prompts.ApplyOverrides 整体替换覆盖集(DB 激活集为权威)
- gateway API: GET/POST /api/v1/prompts、version/activate/deactivate；激活/撤销即广播
- dispatcher/mcp-go: 启动拉激活集 + 订阅热更新(不重启)
- live: 建版本→激活→mcp-go 图谱抽取 2→0→回滚 2(全程不重启)；deactivate 回退代码默认；版本可回溯

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

sundynix-mcp-go/cmd/server/main.go

@@ -98,6 +98,12 @@ func main() {
 	go b.RequestConfigWithRetry(ctx, contract.ConfigKindEmbedding, applyEmbed)
 	go b.RequestConfigWithRetry(ctx, contract.ConfigKindChat, applyChat)
 
+	// Prompt 控制面：拉取激活集覆盖内置默认 + 订阅热更新（管理端激活某版即生效，不重启）。
+	go b.RequestPromptsWithRetry(ctx, prompts.ApplyOverrides)
+	if _, err := b.SubscribePromptsUpdated(prompts.ApplyOverrides); err != nil {
+		log.Printf("[mcp_go] subscribe prompts: %v", err)
+	}
+
 	gw := mcp.NewGateway(b, engine, mem, hist, ragEngine, pgDSN)
 
 	log.Println("[mcp_go] serving MCP over sundynix.tools.go.* (Ctrl-C to quit)")