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/utils/exportBlocksToWord.ts

@@ -77,8 +77,8 @@ function blockToDocxElements(block: ReportBlock, index: number): (Paragraph | Ta
 
     case 'table': {
       const headers = block.headers ?? [];
-      const rows = block.rows ?? [];
-      if (headers.length > 0 || rows.length > 0) {
+      const rawRows = block.rows ?? [];
+      if (headers.length > 0 || (Array.isArray(rawRows) && rawRows.length > 0)) {
         if (block.title) {
           elements.push(
             new Paragraph({
@@ -91,8 +91,15 @@ function blockToDocxElements(block: ReportBlock, index: number): (Paragraph | Ta
         if (headers.length > 0) {
           tableRows.push(makeRow(headers.map(String), true));
         }
-        for (const row of rows) {
-          tableRows.push(makeRow(row.map(c => (c === null || c === undefined ? '-' : String(c)))));
+        const normalizedRows = (Array.isArray(rawRows) ? rawRows : []).map((row: any) => {
+          if (Array.isArray(row)) return row;
+          if (row && typeof row === 'object') {
+            return headers.length > 0 ? headers.map((h: string) => row[h] ?? '') : Object.values(row);
+          }
+          return [String(row ?? '')];
+        });
+        for (const row of normalizedRows) {
+          tableRows.push(makeRow(row.map((c: any) => (c === null || c === undefined ? '-' : String(c)))));
         }
         elements.push(
           new Table({