feat(status): 启用 pg_stat_statements,运行状态页显示最慢 / 最频繁语句与各表死元组;PG 调低 random_page_cost

- docker-compose.yml 的 postgres 加 shared_preload_libraries=pg_stat_statements、pg_stat_statements.track=top;
  要重建 postgres 容器才生效(docs/runbook/storage.md)
- GET /system/storage 的 db.statements:平均最慢(调用 ≥ 10 次)与调用最多各 5 条;没装扩展 / 没预加载时
  enabled=false 并说明原因
- 运行状态页「存储」:体积最大的表加死元组列,新增「数据库语句统计」
- random_page_cost 4 → 1.1(PG_RANDOM_PAGE_COST):库整个在内存里,缺省值高估随机读

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Cxwgnn2pbzQ7rXv3rq7fei

packages/contracts/src/ops.ts

@@ -556,6 +556,16 @@ export const StorageBudgetUsage = z.object({
 });
 export type StorageBudgetUsage = z.infer<typeof StorageBudgetUsage>;
 
+/** 一条语句的累计统计(pg_stat_statements,参数已归一化为 $n) */
+export const StatementStat = z.object({
+  query: z.string(),
+  calls: NonNegInt,
+  totalMs: z.number().nonnegative(),
+  meanMs: z.number().nonnegative(),
+  rows: NonNegInt,
+});
+export type StatementStat = z.infer<typeof StatementStat>;
+
 export const SystemStorage = z.object({
   /** 各项最差档(unknown 不参与) */
   level: HealthLevel,
@@ -578,6 +588,17 @@ export const SystemStorage = z.object({
         lastAnalyzeAt: Timestamp.nullable(),
       }),
     ),
+    /**
+     * 语句统计(pg_stat_statements):enabled=false 时 note 说明原因(没装扩展 / postgres 没预加载);
+     * slowest 按平均耗时(调用 ≥ 10 次),frequent 按调用次数,各前 5;since 为统计起点(上次重置)
+     */
+    statements: z.object({
+      enabled: z.boolean(),
+      note: z.string().nullable(),
+      since: Timestamp.nullable(),
+      slowest: z.array(StatementStat),
+      frequent: z.array(StatementStat),
+    }),
   }),
   /** PG kv_cache 各 region(条数含未清理的过期行) */
   kvCache: z.array(z.object({ region: z.string(), entries: NonNegInt, expired: NonNegInt, bytes: NonNegInt })),