🚀 feat(pagination): unify backend-driven pagination & improve channel tag aggregation

SUMMARY
• Migrated Token, Task, Midjourney, Channel, Redemption tables to true server-side pagination.
• Added total / page / page_size metadata in API responses; switched all affected React tables to consume new structure.
• Implemented counting helpers:
  – model/token.go CountUserTokens
  – model/task.go TaskCountAllTasks / TaskCountAllUserTask
  – model/midjourney.go CountAllTasks / CountAllUserTask
  – model/channel.go CountAllChannels / CountAllTags
• Refactored controllers (token, task, midjourney, channel) for 1-based paging & aggregated returns.
• Redesigned `ChannelsTable.js`:
  – `loadChannels`, `syncPageData`, `enrichChannels` for tag-mode grouping without recursion.
  – Fixed runtime white-screen (maximum call-stack) by removing child duplication.
  – Pagination, search, tag-mode, idSort all hot-reload correctly.
• Removed unused `log` import in controller/midjourney.go.

BREAKING CHANGES
Front-end consumers must now expect data.items / total / page / page_size from list endpoints (`/api/channel`, `/api/task`, `/api/mj`, `/api/token`, etc.).

model/token.go

@@ -320,3 +320,10 @@ func decreaseTokenQuota(id int, quota int) (err error) {
 	).Error
 	return err
 }
+
+// CountUserTokens returns total number of tokens for the given user, used for pagination
+func CountUserTokens(userId int) (int64, error) {
+	var total int64
+	err := DB.Model(&Token{}).Where("user_id = ?", userId).Count(&total).Error
+	return total, err
+}