feat(admin): Add email search and rate limit filtering for accounts and redeem codes

- Add used_by_email column to redeem code export CSV for better user identification
- Implement rate_limited status filter in account listing with RateLimitResetAt check
- Extend redeem code search to include user email in addition to code matching
- Add API key search capability to user listing filters
- Display user email in redeem code table used_by column for improved visibility
- Update search placeholders in UI to reflect expanded search capabilities (email, username, notes, API key)
- Improve Chinese and English localization strings for search hints

backend/internal/repository/user_repo.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	dbent "github.com/Wei-Shaw/sub2api/ent"
+	"github.com/Wei-Shaw/sub2api/ent/apikey"
 	dbuser "github.com/Wei-Shaw/sub2api/ent/user"
 	"github.com/Wei-Shaw/sub2api/ent/userallowedgroup"
 	"github.com/Wei-Shaw/sub2api/ent/usersubscription"
@@ -191,6 +192,7 @@ func (r *userRepository) ListWithFilters(ctx context.Context, params pagination.
 				dbuser.EmailContainsFold(filters.Search),
 				dbuser.UsernameContainsFold(filters.Search),
 				dbuser.NotesContainsFold(filters.Search),
+				dbuser.HasAPIKeysWith(apikey.KeyContainsFold(filters.Search)),
 			),
 		)
 	}