feat(ai): 业务上下文感知与 A2UI 链路统一

- 新增代码内业务上下文元数据层（实体字典 + 三大闭环工作流）
- 新增 get_business_context / get_entity_schema / get_pending_tasks 运行时工具
- SYSTEM_PROMPT 与技能目录改为先查业务流程/待办再执行
- A2UI 增加 ai_a2ui_submissions 幂等表、表单过期、ui.artifact 事件
- 提交回灌携带 submissionId / fieldErrors / 下一步建议
- 前端 uiArtifacts 归一化与过期表单禁用

apps/server/src/agent-context/index.ts

@@ -0,0 +1,12 @@
+export { BusinessContextService } from './business-context.service';
+export { BUSINESS_ENTITIES, BUSINESS_WORKFLOWS } from './business-context.registry';
+export type {
+  BusinessContextPrincipal,
+  BusinessContextResult,
+  BusinessEntity,
+  BusinessEntityField,
+  BusinessEntityRelation,
+  BusinessWorkflow,
+  BusinessWorkflowNextStep,
+  BusinessWorkflowStage,
+} from './business-context.types';