Add PostgreSQL production backend to eliminate SQLite lock contention.

Support DATABASE_URL with connection pooling, pg_dump backups, SQLite migration script, and deploy_postgres.sh with docs.

Co-authored-by: Cursor <cursoragent@cursor.com>

fee_specs.py

@@ -7,13 +7,12 @@
 import json
 import os
 import re
-import sqlite3
 from datetime import datetime
 from typing import Optional
 
 from contract_specs import get_contract_spec
 
-from db_conn import connect_db
+from db_conn import connect_db, is_benign_migration_error
 
 DB_PATH = os.path.join(os.path.dirname(os.path.abspath(__file__)), "futures.db")
 DATA_DIR = os.path.join(os.path.dirname(os.path.abspath(__file__)), "data")
@@ -54,8 +53,9 @@ def ensure_fee_rates_schema(conn=None) -> None:
         ):
             try:
                 conn.execute(sql)
-            except sqlite3.OperationalError:
-                pass
+            except Exception as exc:
+                if not is_benign_migration_error(exc):
+                    raise
         conn.commit()
     finally:
         if close: