feat: Phase 4 — Experiment 自动归档 + 异步 Job（状态机 / SSE / 一键复跑）

- 数据表：job / experiment（spec/result JSON 存档、code_version），Alembic 迁移 53113c80257f
- Job：queued→running→(success|failed) 状态机，BackgroundTasks 本地执行 + 失败兜底标记；结果与 Experiment 关联
- Experiment：每次研究成功自动归档（含 git commit 与收益摘要），支持一键复跑（同 spec 重建 Job）
- API：POST /api/jobs、GET /api/jobs/{id}（内嵌结果）、SSE /api/jobs/{id}/events、/api/experiments 列表/详情/rerun
- 前端：新增「实验」页（列表 / 详情 / 复跑 + Job 轮询）；导航更新
- 端到端验证：真实 20 股 job 提交→后台执行→success→EXP 归档（-12.41%）；executor 成功/失败路径单测
- 测试 73 passed（新增 5 项 Job/Experiment）/ ruff clean / 前端 tsc + build 通过

backend/app/domain/entities/research.py

@@ -8,7 +8,7 @@
 
 from __future__ import annotations
 
-from datetime import date
+from datetime import date, datetime
 
 from pydantic import BaseModel, Field, field_validator, model_validator
 
@@ -167,3 +167,46 @@ class FactorTestReport(BaseModel):
     sample_days: int
     unimplemented: list[str] = Field(default_factory=list)
     config_snapshot: dict = Field(default_factory=dict)
+
+
+# ---------- 异步 Job 与 Experiment（Phase 4） ----------
+
+
+class JobStatus(str):
+    """统一状态机（AGENT.md §20）：queued→running→(success|failed|cancelled)。"""
+
+    QUEUED = "queued"
+    RUNNING = "running"
+    SUCCESS = "success"
+    FAILED = "failed"
+    CANCELLED = "cancelled"
+
+
+class JobRecord(BaseModel):
+    """一次异步研究任务。spec/result 以 JSON 文本存储（保持 Schema 演进自由）。"""
+
+    id: str
+    kind: str  # factor_test | backtest
+    status: str = JobStatus.QUEUED
+    stage: str | None = None
+    spec_json: str
+    error: str | None = None
+    result_json: str | None = None
+    experiment_id: str | None = None
+    created_at: datetime | None = None
+    started_at: datetime | None = None
+    finished_at: datetime | None = None
+
+
+class ExperimentRecord(BaseModel):
+    """一次研究的可复现存档（AGENT.md §21）。"""
+
+    id: str
+    kind: str  # factor_test | backtest
+    spec_json: str
+    result_json: str
+    summary_text: str | None = None  # 便于列表展示的摘要（如 total_return_pct）
+    code_version: str | None = None  # git commit / 代码指纹
+    data_version: str | None = None
+    job_id: str | None = None
+    created_at: datetime | None = None