refactor(db): 抽出 GUID 类型并兼容 SQLite 的 JSONB 字段

- base_class.py 内置 GUID(TypeDecorator)，PostgreSQL 走原生 UUID，
  SQLite 走 CHAR(36)，UUID 在绑定/读取时统一转换。
- study_setup_config 与 study_setup_config_version 改用 JSONB().with_variant
  以便测试库使用 JSON 字段，生产仍保留 JSONB。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/models/study_setup_config.py

@@ -4,12 +4,14 @@ from typing import Optional
 import uuid
 from datetime import datetime
 
-from sqlalchemy import DateTime, ForeignKey, Integer, UniqueConstraint, func
+from sqlalchemy import DateTime, ForeignKey, Integer, JSON, UniqueConstraint, func
 from sqlalchemy.dialects.postgresql import JSONB, UUID
 from sqlalchemy.orm import Mapped, mapped_column
 
 from app.db.base_class import Base
 
+JSONB_TYPE = JSON().with_variant(JSONB, "postgresql")
+
 
 class StudySetupConfig(Base):
     __tablename__ = "study_setup_configs"
@@ -18,10 +20,10 @@ class StudySetupConfig(Base):
     id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
     study_id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), ForeignKey("studies.id"), nullable=False, index=True)
     version: Mapped[int] = mapped_column(Integer, nullable=False, default=1)
-    config: Mapped[dict] = mapped_column(JSONB, nullable=False)
+    config: Mapped[dict] = mapped_column(JSONB_TYPE, nullable=False)
     publish_status: Mapped[str] = mapped_column(default="DRAFT", nullable=False)
-    published_config: Mapped[dict | None] = mapped_column(JSONB, nullable=True)
-    published_project_snapshot: Mapped[dict | None] = mapped_column(JSONB, nullable=True)
+    published_config: Mapped[dict | None] = mapped_column(JSONB_TYPE, nullable=True)
+    published_project_snapshot: Mapped[dict | None] = mapped_column(JSONB_TYPE, nullable=True)
     current_branch_name: Mapped[str] = mapped_column(nullable=False, default="main")
     active_branch_base_version_id: Mapped[Optional[uuid.UUID]] = mapped_column(
         UUID(as_uuid=True), ForeignKey("study_setup_config_versions.id", ondelete="SET NULL"), nullable=True