fix: ChatCitation 字段 + BigInt 类型修复

- ChatCitation.content → excerptText（对齐 Prisma schema）
- ChatCitation.score 不存在→ 移除
- UploadedFile.sizeBytes BigInt → Number() 转换

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/modules/rag-chat/rag-chat.service.ts

@@ -94,8 +94,8 @@ export class RagChatService {
         data: {
           messageId: aiMsg.id,
           chunkId: c.id,
-          content: c.text.slice(0, 500),
+          sourceTitle: c.title ?? null,
-          score: c.score ?? 0,
+          excerptText: c.text.slice(0, 500),
         },
       });
     }

src/modules/users/users.service.ts

@@ -76,7 +76,7 @@ export class UsersService {
       where: { userId },
       select: { sizeBytes: true, mimeType: true },
     });
-    const usedBytes = files.reduce((sum, f) => sum + f.sizeBytes, 0);
+    const usedBytes = files.reduce((sum, f) => sum + Number(f.sizeBytes), 0);
     const totalBytes = 1024 * 1024 * 1024; // 1GB hardcoded for now
     return { totalBytes, usedBytes, fileCount: files.length };
   }