feat: add PostgreSQL database backend support

Add multi-database support allowing selection between SQL Server and
PostgreSQL via database.active config. Changes include dialect-aware
SQL generation, cross-database timestamp functions, PostgreSQL connection
URL builder, and psycopg dependency.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/services/box_service.py

@@ -25,11 +25,7 @@ class DuplicateBoxItemError(Exception):
 
 def query_erp_info(db: Session, zongpai_no: str) -> dict:
     """从 ERP 视图查询总排号对应的排产号和数量。"""
-    sql = text(
-        "SELECT TOP 1 [总排号], [排产号], [数量] "
-        "FROM [ERPAuto].[vw_productionContractData] "
-        "WHERE [总排号] = :zongpai_no"
-    )
+    sql = text(_erp_info_sql(db))
     row = db.execute(sql, {"zongpai_no": zongpai_no}).fetchone()
     if not row:
         raise ZongpaiNotFoundError()
@@ -40,6 +36,22 @@ def query_erp_info(db: Session, zongpai_no: str) -> dict:
     }
 
 
+def _erp_info_sql(db: Session) -> str:
+    dialect_name = db.bind.dialect.name if db.bind is not None else ""
+    if dialect_name == "postgresql":
+        return (
+            'SELECT "总排号", "排产号", "数量" '
+            'FROM "ERPAuto"."vw_productionContractData" '
+            'WHERE "总排号" = :zongpai_no '
+            "LIMIT 1"
+        )
+    return (
+        "SELECT TOP 1 [总排号], [排产号], [数量] "
+        "FROM [ERPAuto].[vw_productionContractData] "
+        "WHERE [总排号] = :zongpai_no"
+    )
+
+
 def get_box_info(db: Session, zongpai_no: str) -> dict:
     """获取装箱信息：排产号、数量、已有箱号明细。"""
     zongpai_no = zongpai_no.strip().upper()