refactor: 降级 Drizzle ORM 至 0.45.x 稳定版，对齐 Better Auth 兼容性

- drizzle-orm 1.0.0-beta.15 → 0.45.2, drizzle-kit → 0.31.10
- RQBv2 defineRelations() → 旧版 relations() 回调语法
- drizzle-orm/zod → drizzle-zod 独立包
- auth/schema.ts 改由 Better Auth CLI 生成（bun run db:auth）
- db/schema/index.ts 选择性导出表（不导出生成文件中的旧版 relations）
- 删除 db:push script，强制 db:generate → db:migrate 工作流
- 重建迁移基线（删除旧迁移目录，全新生成初始迁移）

package.json

@@ -43,8 +43,9 @@
     "@tanstack/react-start": "^1.167.6",
     "@types/bun": "^1.3.11",
     "@vitejs/plugin-react": "^6.0.1",
-    "drizzle-kit": "1.0.0-beta.15-859cf75",
-    "drizzle-orm": "1.0.0-beta.15-859cf75",
+    "drizzle-kit": "^0.31.10",
+    "drizzle-orm": "^0.45.2",
+    "drizzle-zod": "^0.7.1",
     "nitro": "npm:nitro-nightly@3.0.1-20260324-103046-9ce219ca",
     "postgres": "^3.4.8",
     "react": "^19.2.4",