日K加载提速：adj_factor 覆盖索引 + 冷路径并发 + 热路径进程内缓存直返

- adj_factor 覆盖索引 (ts_code,trade_date) INCLUDE (adj_factor)：根治堆碎片化
  （单股 6516 行散 6516 块，满载时位图堆扫 1.5s+），Index Only Scan ~2ms；
  因子查询全部改 2 列投影，lag() 窗口只取变点（6516→32 行）
- preview 冷路径 2 会话 2 波并发，信息卡合并为 LEFT JOIN LATERAL 一条
- 鉴权会话 60s 进程内缓存（登出/全端登出即时失效），全站请求省 ~80ms
- pvj/chipsj/stocksj/facetsj 存 model_dump_json 原串直返（与 response_model
  字节一致），热路径 230-2190ms → 1-2ms；get_version 本地缓存+bump 即时可见
- 连接池 10+20；smoke_test 适配鉴权缓存

backend/alembic/versions/20260902_01_adj_factor_cover.py

@@ -0,0 +1,49 @@
+"""adj_factor 覆盖索引：因子查询免堆访问（碎片免疫）
+
+Revision ID: 20260902_01
+Revises: 20260815_04
+Create Date: 2026-09-02
+"""
+from typing import Sequence, Union
+
+from alembic import op
+
+revision: str = "20260902_01"
+down_revision: Union[str, Sequence[str], None] = "20260815_04"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    # CONCURRENTLY / VACUUM 不能在事务内执行；autocommit_block 内每条语句独立提交
+    with op.get_context().autocommit_block():
+        op.create_index(
+            "ix_adj_code_date_cover",
+            "adj_factor",
+            ["ts_code", "trade_date"],
+            postgresql_concurrently=True,
+            postgresql_include=["adj_factor"],
+        )
+        # ts_code 单列索引被覆盖索引取代（同前缀），删掉省写放大
+        op.drop_index(
+            "ix_adj_factor_ts_code",
+            table_name="adj_factor",
+            postgresql_concurrently=True,
+        )
+        # 刷可见性映射（Index Only Scan 的前提）+ 更新统计信息；低峰执行（3.2GB 表数十秒）
+        op.execute("VACUUM (ANALYZE) adj_factor")
+
+
+def downgrade() -> None:
+    with op.get_context().autocommit_block():
+        op.create_index(
+            "ix_adj_factor_ts_code",
+            "adj_factor",
+            ["ts_code"],
+            postgresql_concurrently=True,
+        )
+        op.drop_index(
+            "ix_adj_code_date_cover",
+            table_name="adj_factor",
+            postgresql_concurrently=True,
+        )