feat: 同IP默认账号配额改为 primaryCount × 2

- 动态计算该类型默认账号数量 primaryCount
- 前 primaryCount × 2 次在同IP的两个默认账号间轮询
- 超限后再去其他非默认账号
- 无默认账号时 threshold=0, 直接走轮询

packages/backend/src/cloud/credential.service.ts

@@ -456,8 +456,15 @@ export async function getAndValidateCredential(cloudType: string, ipAddress?: st
 
     const ipTodayCount = ipCountRow?.total || 0;
 
-    if (ipTodayCount < 3) {
-      // First 2 saves — use a primary account (is_primary=1), fallback to any healthy
+    // How many primary accounts does this cloud type have?
+    const primaryCountRow = db.prepare(
+      `SELECT COUNT(*) as c FROM cloud_configs WHERE cloud_type = ? AND is_primary = 1 AND is_active = 1`
+    ).get(cloudType) as { c: number };
+    const primaryCount = primaryCountRow?.c || 0;
+    const primaryThreshold = primaryCount * 2; // Each primary account gets 2 uses per IP
+
+    if (ipTodayCount < primaryThreshold) {
+      // First N saves (primaryCount × 2) — use primary accounts (is_primary=1), fallback to any healthy
       config = db.prepare(
         `SELECT * FROM cloud_configs
          WHERE cloud_type = ? AND is_active = 1
@@ -466,7 +473,7 @@ export async function getAndValidateCredential(cloudType: string, ipAddress?: st
          LIMIT 1`
       ).get(cloudType) as CloudConfig | undefined;
     } else {
-      // 3rd+ save — exclude accounts this IP has already used today,
+      // After primary threshold — exclude accounts this IP has already used today,
       // fall back to other available accounts round-robin
       const usedConfigIds = db.prepare(
         `SELECT DISTINCT config_id FROM ip_daily_save_counts