feat(ssa): Complete Phase V-A editable analysis plan variables

Features:
- Add editable variable selection in workflow plan (SingleVarSelect + MultiVarTags)
- Implement 3-layer flexible interception (warning bar + icon + blocking dialog)
- Add tool_param_constraints.json for 12 statistical tools parameter validation
- Add PATCH /workflow/:id/params API with Zod structural validation
- Implement synchronous parameter sync before execution (Promise chaining)
- Fix LLM hallucination by strict system prompt constraints
- Fix DynamicReport object-based rows compatibility (R baseline_table)
- Fix Word export row.map error with same normalization logic
- Restore inferGroupingVar for smart default variable selection
- Add ReactMarkdown rendering in SSAChatPane
- Update SSA module status document to v3.5

Modified files:
- backend: workflow.routes, ChatHandlerService, SystemPromptService, FlowTemplateService
- frontend: WorkflowTimeline, SSAWorkspacePane, DynamicReport, SSAChatPane, ssaStore, ssa.css
- config: tool_param_constraints.json (new)
- docs: SSA status doc, team review reports

Tested: Cohort study end-to-end execution + report export verified
Co-authored-by: Cursor <cursoragent@cursor.com>

frontend-v2/src/modules/ssa/hooks/useSSAChat.ts

@@ -239,18 +239,20 @@ export function useSSAChat(): UseSSAChatReturn {
             }
 
             // analysis_plan 事件（Phase IV: 对话驱动分析）
+            // 仅创建记录，不打开工作区 — 等用户确认方案后再打开
             if (parsed.type === 'analysis_plan' && parsed.plan) {
               const plan = parsed.plan as WorkflowPlan;
-              const { addRecord, setActivePane, setWorkspaceOpen } = useSSAStore.getState();
+              const { addRecord } = useSSAStore.getState();
               addRecord(content, plan);
-              setActivePane('sap');
-              setWorkspaceOpen(true);
               continue;
             }
 
-            // plan_confirmed 事件（Phase IV: 用户确认方案后触发执行）
-            if (parsed.type === 'plan_confirmed' && parsed.workflowId) {
-              setPendingPlanConfirm({ workflowId: parsed.workflowId });
+            // plan_confirmed 事件（Phase IV: 用户确认方案后打开工作区）
+            // 不自动触发 executeWorkflow — 由用户在工作区手动点击「开始执行分析」
+            if (parsed.type === 'plan_confirmed') {
+              const { setActivePane, setWorkspaceOpen } = useSSAStore.getState();
+              setActivePane('sap');
+              setWorkspaceOpen(true);
               setPendingQuestion(null);
               continue;
             }
@@ -319,14 +321,27 @@ export function useSSAChat(): UseSSAChatReturn {
 
   /**
    * 响应 ask_user 卡片（Phase III）
+   * 将 value 解析为中文 label 用于显示
    */
   const respondToQuestion = useCallback(async (sessionId: string, response: AskUserResponseData) => {
+    const question = pendingQuestion;
     setPendingQuestion(null);
-    const displayText = response.action === 'select'
-      ? `选择了: ${response.selectedValues?.join(', ')}`
-      : response.freeText || '(已回复)';
+
+    let displayText: string;
+    if (response.action === 'select' && response.selectedValues) {
+      const labels = response.selectedValues.map(val => {
+        const opt = question?.options?.find(o => o.value === val);
+        return opt?.label || val;
+      });
+      displayText = `选择了 ${labels.join('、')}`;
+    } else if (response.action === 'free_text') {
+      displayText = response.freeText || '(已回复)';
+    } else {
+      displayText = '(已回复)';
+    }
+
     await sendChatMessage(sessionId, displayText, { askUserResponse: response });
-  }, [sendChatMessage]);
+  }, [sendChatMessage, pendingQuestion]);
 
   /**
    * H1: 跳过 ask_user 卡片
@@ -337,7 +352,7 @@ export function useSSAChat(): UseSSAChatReturn {
       questionId,
       action: 'skip',
     };
-    await sendChatMessage(sessionId, '跳过了此问题', { askUserResponse: skipResponse });
+    await sendChatMessage(sessionId, '已跳过此问题', { askUserResponse: skipResponse });
   }, [sendChatMessage]);
 
   return {