refactor: migrate API keys to config, extend Kline intervals, add DB extensions

Security:
- Move hardcoded Binance API key/secret from rest.ts to env.yaml (exchange config segment)
- Add ExchangeConfig validation in config/validators.ts
- Export typed exchange config from config/index.ts
- Update AGENTS/07-caveats.md to reflect the new policy

Kline intervals (add 3m / 2h / 6h / 8h / 1mon):
- TypeScript: update KlineInterval type, KLINE_INTERVAL_MS mapping, build_aggregates_sql refresh chain
- Python: sync KlineInterval Literal type, INTERVAL_TO_TABLE and INTERVAL_MS mappings, db_test table list
- SQL: add 5 continuous aggregate materialized views (klines_3m/2h/6h/8h/1mon) with indexes
- SQL: extend default kline_intervals in trading_pairs table
- SQL: add cross-sectional query indexes for klines_1d and klines_1w

DB:
- Enable pg_prewarm extension (backtest warmup)
- Enable pg_stat_statements extension (slow query monitoring)

Other:
- data/run/exchange.ts: graceful pgsql shutdown after backfill completes
- Config path: load from data/env.yaml (symlink) instead of project root

data/db/init-db/01-timescaledb.sql

@@ -13,12 +13,18 @@
 --   - klines 基表由 02-init-tables.sql 创建为 TimescaleDB hypertable
 --   - 连续聚合视图由 03-continuous-aggregates.sql 创建
 --   - TypeORM 的 synchronize:true 与 SQL 脚本互为 fallback（开发/生产双路径）
---   - 本脚本为 init-db 链的第一环，仅负责扩展启用
+--   - 本脚本为 init-db 链的第一环，负责扩展启用（TimescaleDB / pg_prewarm / pg_stat_statements）
 -- ============================================================
 
 -- 启用 TimescaleDB 扩展（必须最先执行）
 CREATE EXTENSION IF NOT EXISTS timescaledb CASCADE;
 
+-- 启用 pg_prewarm 扩展（回测预热，减少首轮查询延迟）
+CREATE EXTENSION IF NOT EXISTS pg_prewarm;
+
+-- 启用 pg_stat_statements 扩展（慢查询监控，零成本）
+CREATE EXTENSION IF NOT EXISTS pg_stat_statements;
+
 -- 验证扩展已启用
 DO $$
 BEGIN