feat(admin): Implement System Knowledge Base management module

Features:

- Backend: SystemKbService with full CRUD (knowledge bases + documents)

- Backend: 8 RESTful API endpoints (list/detail/create/update/delete/upload/download)

- Backend: OSS storage integration (system/knowledge-bases/{kbId}/{docId})

- Backend: RAG engine integration (document parsing, chunking, vectorization)

- Frontend: SystemKbListPage with card-based layout

- Frontend: SystemKbDetailPage with document management table

- Frontend: Master-Detail UX pattern for better user experience

- Document upload (single/batch), download (preserving original filename), delete

Technical:

- Database migration for system_knowledge_bases and system_kb_documents tables

- OSSAdapter.getSignedUrl with Content-Disposition for original filename

- Reuse RAG engine from common/rag for document processing

Tested: Local environment verified, all features working

backend/test-oss-upload.cjs

@@ -0,0 +1,104 @@
+/**
+ * OSS 上传下载完整性测试
+ * 
+ * 测试流程：
+ * 1. 读取本地 PDF 文件
+ * 2. 上传到 OSS
+ * 3. 从 OSS 下载
+ * 4. 比较 MD5 值
+ */
+
+require('dotenv').config();
+const fs = require('fs');
+const crypto = require('crypto');
+const OSS = require('ali-oss');
+
+const testFile = 'D:\\MyCursor\\AIclinicalresearch\\docs\\06-测试文档\\近红外光谱（NIRS）队列研究举例.pdf';
+const testKey = 'test/oss-integrity-test.pdf';
+
+async function main() {
+  console.log('='.repeat(60));
+  console.log('OSS Upload/Download Integrity Test');
+  console.log('='.repeat(60));
+
+  // 1. 读取本地文件
+  console.log('\n[1] Reading local file...');
+  const localBuffer = fs.readFileSync(testFile);
+  const localMd5 = crypto.createHash('md5').update(localBuffer).digest('hex');
+  console.log(`  File size: ${localBuffer.length} bytes`);
+  console.log(`  MD5: ${localMd5}`);
+  console.log(`  First 20 bytes: ${localBuffer.slice(0, 20).toString('hex')}`);
+
+  // 2. 创建 OSS 客户端
+  console.log('\n[2] Creating OSS client...');
+  const client = new OSS({
+    region: process.env.OSS_REGION,
+    bucket: process.env.OSS_BUCKET,
+    accessKeyId: process.env.OSS_ACCESS_KEY_ID,
+    accessKeySecret: process.env.OSS_ACCESS_KEY_SECRET,
+    endpoint: `${process.env.OSS_REGION}.aliyuncs.com`,
+    secure: true,
+  });
+  console.log(`  Region: ${process.env.OSS_REGION}`);
+  console.log(`  Bucket: ${process.env.OSS_BUCKET}`);
+
+  // 3. 上传到 OSS
+  console.log('\n[3] Uploading to OSS...');
+  try {
+    const uploadResult = await client.put(testKey, localBuffer, {
+      headers: {
+        'Content-Type': 'application/pdf',
+      },
+    });
+    console.log(`  Upload success: ${uploadResult.name}`);
+  } catch (error) {
+    console.error(`  Upload failed:`, error.message);
+    return;
+  }
+
+  // 4. 从 OSS 下载
+  console.log('\n[4] Downloading from OSS...');
+  try {
+    const downloadResult = await client.get(testKey);
+    const downloadBuffer = downloadResult.content;
+    const downloadMd5 = crypto.createHash('md5').update(downloadBuffer).digest('hex');
+    
+    console.log(`  Download size: ${downloadBuffer.length} bytes`);
+    console.log(`  MD5: ${downloadMd5}`);
+    console.log(`  First 20 bytes: ${downloadBuffer.slice(0, 20).toString('hex')}`);
+
+    // 5. 比较
+    console.log('\n[5] Comparing...');
+    if (localMd5 === downloadMd5) {
+      console.log('  ✅ MD5 MATCH - File integrity OK!');
+    } else {
+      console.log('  ❌ MD5 MISMATCH - File corrupted!');
+      console.log(`     Local:    ${localMd5}`);
+      console.log(`     Download: ${downloadMd5}`);
+    }
+
+    // 保存下载的文件用于对比
+    const outputPath = 'D:\\MyCursor\\AIclinicalresearch\\docs\\06-测试文档\\oss-downloaded-test.pdf';
+    fs.writeFileSync(outputPath, downloadBuffer);
+    console.log(`\n  Downloaded file saved to: ${outputPath}`);
+
+  } catch (error) {
+    console.error(`  Download failed:`, error.message);
+    return;
+  }
+
+  // 6. 清理
+  console.log('\n[6] Cleanup...');
+  try {
+    await client.delete(testKey);
+    console.log('  Test file deleted from OSS');
+  } catch (error) {
+    console.log(`  Cleanup failed: ${error.message}`);
+  }
+
+  console.log('\n' + '='.repeat(60));
+  console.log('Test Complete!');
+  console.log('='.repeat(60));
+}
+
+main().catch(console.error);