feat(ssa): Complete Phase 2A frontend integration - multi-step workflow end-to-end

Phase 2A: WorkflowPlannerService, WorkflowExecutorService, Python data quality, 6 bug fixes, DescriptiveResultView, multi-step R code/Word export, MVP UI reuse. V11 UI: Gemini-style, multi-task, single-page scroll, Word export. Architecture: Block-based rendering consensus (4 block types). New R tools: chi_square, correlation, descriptive, logistic_binary, mann_whitney, t_test_paired. Docs: dev summary, block-based plan, status updates, task list v2.0.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/prisma/schema.prisma

@@ -2153,12 +2153,14 @@ model SsaSession {
   dataSchema    Json?    @map("data_schema")    /// 数据结构（LLM可见）
   dataPayload   Json?    @map("data_payload")   /// 真实数据（仅R可见）
   dataOssKey    String?  @map("data_oss_key")   /// OSS 存储 key（大数据）
+  dataProfile   Json?    @map("data_profile")   /// 🆕 Python 生成的 DataProfile（Phase 2A）
   status        String   @default("active")     /// active | consult | completed | error
   createdAt     DateTime @default(now()) @map("created_at")
   updatedAt     DateTime @updatedAt @map("updated_at")
   
   messages      SsaMessage[]
   executionLogs SsaExecutionLog[]
+  workflows     SsaWorkflow[]                   /// 🆕 多步骤流程（Phase 2A）
   
   @@index([userId], map: "idx_ssa_session_user")
   @@index([status], map: "idx_ssa_session_status")
@@ -2306,3 +2308,54 @@ model SsaInterpretation {
   @@map("ssa_interpretation_templates")
   @@schema("ssa_schema")
 }
+
+// ============================================================
+// 🆕 Phase 2A 新增：多步骤流程管理
+// ============================================================
+
+/// SSA 多步骤流程
+model SsaWorkflow {
+  id              String    @id @default(uuid())
+  sessionId       String    @map("session_id")
+  messageId       String?   @map("message_id")      /// 关联的计划消息
+  status          String    @default("pending")     /// pending | running | completed | partial | error
+  totalSteps      Int       @map("total_steps")
+  completedSteps  Int       @default(0) @map("completed_steps")
+  workflowPlan    Json      @map("workflow_plan")   /// 原始计划 JSON
+  reasoning       String?   @db.Text                /// LLM 规划理由
+  createdAt       DateTime  @default(now()) @map("created_at")
+  startedAt       DateTime? @map("started_at")
+  completedAt     DateTime? @map("completed_at")
+  
+  session         SsaSession @relation(fields: [sessionId], references: [id], onDelete: Cascade)
+  steps           SsaWorkflowStep[]
+  
+  @@index([sessionId], map: "idx_ssa_workflow_session")
+  @@index([status], map: "idx_ssa_workflow_status")
+  @@map("ssa_workflows")
+  @@schema("ssa_schema")
+}
+
+/// SSA 流程步骤
+model SsaWorkflowStep {
+  id              String    @id @default(uuid())
+  workflowId      String    @map("workflow_id")
+  stepOrder       Int       @map("step_order")       /// 步骤顺序（1, 2, 3...）
+  toolCode        String    @map("tool_code")
+  toolName        String    @map("tool_name")
+  status          String    @default("pending")      /// pending | running | success | warning | error | skipped
+  inputParams     Json?     @map("input_params")     /// 输入参数
+  guardrailChecks Json?     @map("guardrail_checks") /// JIT 护栏检验结果
+  outputResult    Json?     @map("output_result")    /// 执行结果
+  errorInfo       Json?     @map("error_info")       /// 错误信息
+  executionMs     Int?      @map("execution_ms")     /// 执行耗时（毫秒）
+  startedAt       DateTime? @map("started_at")
+  completedAt     DateTime? @map("completed_at")
+  
+  workflow        SsaWorkflow @relation(fields: [workflowId], references: [id], onDelete: Cascade)
+  
+  @@index([workflowId], map: "idx_ssa_workflow_step_workflow")
+  @@index([status], map: "idx_ssa_workflow_step_status")
+  @@map("ssa_workflow_steps")
+  @@schema("ssa_schema")
+}