feat(ssa): Implement dual-channel architecture Phase 1-3 (QPER + LLM Agent pipeline)

Completed:
- Phase 1: DB schema (execution_mode + ssa_agent_executions), ModeToggle component, Session PATCH API
- Phase 2: AgentPlannerService + AgentCoderService (streaming) + CodeRunnerService + R Docker /execute-code endpoint
- Phase 3: AgentCodePanel (3-step confirmation UI), SSE event handling (7 agent events), streaming code display
- Three-step confirmation pipeline: plan -> user confirm -> stream code -> user confirm -> execute R code -> results
- R Docker sandbox /execute-code endpoint with 120s timeout + block_helpers preloaded
- E2E dual-channel test script (8 tests)
- Updated R engine architecture doc (v1.5) and SSA module status doc (v4.0)

Technical details:
- AgentCoderService uses LLM streaming (chatStream) for real-time code generation feedback
- ReviewerAgent temporarily disabled, prioritizing Plan -> Code -> Execute flow
- CodeRunnerService wraps user code with auto data loading (df variable injection)
- Frontend handles agent_planning, agent_plan_ready, code_generating, code_generated, code_executing, code_result events
- ask_user mechanism used for plan and code confirmation steps

Files: 24 files (4 new services, 2 new components, 1 migration, 1 E2E test, 16 modified)
Made-with: Cursor

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

@@ -257,6 +257,88 @@ export function useSSAChat(): UseSSAChatReturn {
               continue;
             }
 
+            // ── Agent 通道 SSE 事件 ──
+
+            if (parsed.type === 'agent_planning') {
+              const { setAgentExecution, setWorkspaceOpen, setActivePane } = useSSAStore.getState();
+              setAgentExecution({
+                id: parsed.executionId || crypto.randomUUID(),
+                sessionId: '',
+                query: content,
+                retryCount: 0,
+                status: 'planning',
+              });
+              setActivePane('execution');
+              setWorkspaceOpen(true);
+              continue;
+            }
+
+            if (parsed.type === 'agent_plan_ready') {
+              const { updateAgentExecution } = useSSAStore.getState();
+              updateAgentExecution({
+                planText: parsed.planText,
+                planSteps: parsed.plan?.steps,
+                status: 'plan_pending',
+              });
+              continue;
+            }
+
+            if (parsed.type === 'code_generating') {
+              const { updateAgentExecution } = useSSAStore.getState();
+              updateAgentExecution({
+                partialCode: parsed.partialCode,
+                status: 'coding',
+              });
+              continue;
+            }
+
+            if (parsed.type === 'code_generated') {
+              const { updateAgentExecution } = useSSAStore.getState();
+              updateAgentExecution({
+                generatedCode: parsed.code,
+                partialCode: undefined,
+                status: parsed.code ? 'code_pending' : 'coding',
+              });
+              continue;
+            }
+
+            if (parsed.type === 'code_executing') {
+              const { updateAgentExecution } = useSSAStore.getState();
+              updateAgentExecution({ status: 'executing' });
+              continue;
+            }
+
+            if (parsed.type === 'code_result') {
+              const { updateAgentExecution } = useSSAStore.getState();
+              updateAgentExecution({
+                reportBlocks: parsed.reportBlocks,
+                generatedCode: parsed.code || useSSAStore.getState().agentExecution?.generatedCode,
+                status: 'completed',
+                durationMs: parsed.durationMs,
+              });
+              continue;
+            }
+
+            if (parsed.type === 'code_error') {
+              const { updateAgentExecution } = useSSAStore.getState();
+              updateAgentExecution({
+                status: 'error',
+                errorMessage: parsed.message,
+              });
+              continue;
+            }
+
+            if (parsed.type === 'code_retry') {
+              const { updateAgentExecution } = useSSAStore.getState();
+              updateAgentExecution({
+                status: 'coding',
+                retryCount: parsed.retryCount || 0,
+                generatedCode: parsed.code,
+                errorMessage: undefined,
+              });
+              continue;
+            }
+
             // 错误事件
             if (parsed.type === 'error') {
               const errMsg = parsed.message || '处理消息时发生错误';