feat: 新增OSS直传迁移能力，实现图片从本地到OSS的迁移流程

1.  新增OSS直传工具类函数，实现带凭据校验的PUT/HEAD请求
2.  新增oss_migration_log数据表，用于跟踪迁移状态
3.  重构图片保存逻辑，优先上传OSS失败则降级本地并登记补传任务
4.  新增批量迁移脚本，支持状态查看、断点续传、校验和回写DB
5.  新增OSS直链抽查调试脚本

dev_test_scripts/debug/debug_oss_spot_check.js

@@ -0,0 +1,26 @@
+// 抽查 OSS 直链是否可公共读：每个库取 1 条 oss_url 做 GET，打印状态码与字节数
+'use strict'
+const path = require('path')
+const https = require('https')
+const Database = require('better-sqlite3')
+
+const db = new Database(path.resolve(__dirname, '..', '..', 'data', 'style_check.db'))
+const libs = ['item_images', 'wave', 'korean', 'x_fashion']
+
+const get = (url) => new Promise((resolve, reject) => {
+  https.get(url, res => {
+    let n = 0
+    res.on('data', c => { n += c.length })
+    res.on('end', () => resolve({ status: res.statusCode, bytes: n }))
+  }).on('error', reject)
+})
+
+;(async () => {
+  for (const lib of libs) {
+    const r = db.prepare('SELECT local_path, oss_url FROM oss_migration_log WHERE lib=? LIMIT 1').get(lib)
+    if (!r) { console.log(lib, '无记录'); continue }
+    const res = await get(r.oss_url)
+    console.log(`${lib} -> ${res.status} ${res.bytes} bytes  ${r.oss_url}`)
+  }
+  db.close()
+})()