feat(phase2): shared/ 共享层迁移

- shared/: enums/constants/pagination/base_model/base_db/base_repository/base_service
- apps/constants 与 apps/models/base_model、base_db 改为垫片
- 新增 pagination 单元测试

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

tests/unit/core/test_pagination.py

@@ -0,0 +1,21 @@
+"""shared/pagination.py 分页工具单元测试。"""
+
+from shared.pagination import get_page_params
+
+
+def test_defaults():
+    page, size = get_page_params({})
+    assert page == 1
+    assert size == 10
+
+
+def test_valid_params():
+    page, size = get_page_params({"pageNo": "3", "pageSize": "20"})
+    assert page == 3
+    assert size == 20
+
+
+def test_invalid_params_fall_back():
+    page, size = get_page_params({"pageNo": "abc", "pageSize": "0"})
+    assert page == 1
+    assert size == 10