feat: IP-based daily account priority for save

- Added ip_daily_save_counts table to track per-IP daily usage

 - getAndValidateCredential now accepts ipAddress parameter

 - First 2 saves by same IP use primary account; 3rd+ round-robins to other accounts

 - Counter increments on each successful credential acquisition

 - All timestamps in Asia/Shanghai timezone

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

@@ -141,7 +141,7 @@ async function doSaveFromShare(shareUrl: string, cloudType: string, sourceTitle?
   }
 
   // ── Unified credential validation ──
-  const credential = await getAndValidateCredential(cloudType);
+  const credential = await getAndValidateCredential(cloudType, ipAddress);
   if (!credential.valid || !credential.config) {
     return { success: false, message: credential.message };
   }

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

@@ -397,16 +397,79 @@ export interface CredentialValidationResult {
  * 
  * Reference: search-ucmao get_and_validate_credential() pattern.
  */
-export async function getAndValidateCredential(cloudType: string): Promise<CredentialValidationResult> {
+export async function getAndValidateCredential(cloudType: string, ipAddress?: string): Promise<CredentialValidationResult> {
   const db = getDb();
 
-  const config = db.prepare(
-    `SELECT * FROM cloud_configs
-     WHERE cloud_type = ? AND is_active = 1
-     AND consecutive_failures < 5
-     ORDER BY last_used_at ASC NULLS FIRST
-     LIMIT 1`
-  ).get(cloudType) as CloudConfig | undefined;
+  let config: CloudConfig | undefined;
+
+  if (!ipAddress) {
+    // No IP info — fallback to simple LUR
+    config = db.prepare(
+      `SELECT * FROM cloud_configs
+       WHERE cloud_type = ? AND is_active = 1
+       AND consecutive_failures < 5
+       ORDER BY last_used_at ASC NULLS FIRST
+       LIMIT 1`
+    ).get(cloudType) as CloudConfig | undefined;
+  } else {
+    // Get today's date in Shanghai time
+    const today = (() => {
+      const now = new Date();
+      const shanghai = new Date(now.toLocaleString('en-US', { timeZone: 'Asia/Shanghai' }));
+      return shanghai.toISOString().slice(0, 10);
+    })();
+
+    // Count how many times this IP has saved today for this cloud type
+    const ipCountRow = db.prepare(
+      `SELECT COALESCE(SUM(save_count), 0) as total
+       FROM ip_daily_save_counts
+       WHERE ip_address = ? AND date = ? AND cloud_type = ?`
+    ).get(ipAddress, today, cloudType) as { total: number };
+
+    const ipTodayCount = ipCountRow?.total || 0;
+
+    if (ipTodayCount < 3) {
+      // First 2 saves — use the primary account (least recently used, healthy)
+      config = db.prepare(
+        `SELECT * FROM cloud_configs
+         WHERE cloud_type = ? AND is_active = 1
+         AND consecutive_failures < 5
+         ORDER BY last_used_at ASC NULLS FIRST
+         LIMIT 1`
+      ).get(cloudType) as CloudConfig | undefined;
+    } else {
+      // 3rd+ save — 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
+         WHERE ip_address = ? AND date = ? AND cloud_type = ?
+         ORDER BY config_id`
+      ).all(ipAddress, today, cloudType) as { config_id: number }[];
+
+      const usedIds = usedConfigIds.map(r => r.config_id);
+      const placeholders = usedIds.length > 0 ? usedIds.map(() => '?').join(',') : '-1';
+
+      config = db.prepare(
+        `SELECT * FROM cloud_configs
+         WHERE cloud_type = ? AND is_active = 1
+         AND consecutive_failures < 5
+         AND id NOT IN (${placeholders})
+         ORDER BY last_used_at ASC NULLS FIRST
+         LIMIT 1`
+      ).get(cloudType, ...usedIds) as CloudConfig | undefined;
+
+      // If all accounts have been used by this IP, fall back to primary
+      if (!config) {
+        config = db.prepare(
+          `SELECT * FROM cloud_configs
+           WHERE cloud_type = ? AND is_active = 1
+           AND consecutive_failures < 5
+           ORDER BY last_used_at ASC NULLS FIRST
+           LIMIT 1`
+        ).get(cloudType) as CloudConfig | undefined;
+      }
+    }
+  }
 
   if (!config) {
     return {
@@ -457,6 +520,21 @@ export async function getAndValidateCredential(cloudType: string): Promise<Crede
       };
     }
 
+    // Track IP daily usage count (if ipAddress provided)
+    if (ipAddress && config) {
+      const today = (() => {
+        const now = new Date();
+        const shanghai = new Date(now.toLocaleString('en-US', { timeZone: 'Asia/Shanghai' }));
+        return shanghai.toISOString().slice(0, 10);
+      })();
+      db.prepare(
+        `INSERT INTO ip_daily_save_counts (ip_address, date, cloud_type, config_id, save_count)
+         VALUES (?, ?, ?, ?, 1)
+         ON CONFLICT(ip_address, date, cloud_type, config_id)
+         DO UPDATE SET save_count = save_count + 1`
+      ).run(ipAddress, today, cloudType, config.id);
+    }
+
     return {
       valid: true,
       config: { ...config, cookie: decryptedCookie },