feat: unified gravity system - VIP members consume gravity instead of unlimited; add monthly gravity top-up cron

backend/src/modules/share/share.service.ts

@@ -83,8 +83,11 @@ export class ShareService {
 
     if (todayCredited >= DAILY_LIMIT) return { dailyLimitReached: true, visitorUserId }
 
-    const shareCreditsResult = await this.quotaService.grantShareCredits(sharerIdStr)
-    if (!shareCreditsResult) return { creditFailed: true, visitorUserId }
+    try {
+      await this.quotaService.grantGravity(sharerIdStr, 1)
+    } catch (e) {
+      return { creditFailed: true, visitorUserId }
+    }
 
     await this.visitModel.updateOne(
       { shareId: share._id, visitorId },
@@ -125,7 +128,7 @@ export class ShareService {
       totalVisits: visitAgg[0]?.totalVisits ?? 0,
       creditedCount: visitAgg[0]?.creditedCount ?? 0,
       todayCredited: todayAgg,
-      shareCredits: user?.shareCredits ?? 0,
+      gravity: user?.gravity ?? 0,
     }
   }