Fix ToggleReaction error handling - use pgx.ErrNoRows instead of sql.ErrNoRows

pgx returns pgx.ErrNoRows not sql.ErrNoRows for no rows result set, causing toggle reaction to fail

go-backend/internal/repository/post_repository.go

@@ -2,10 +2,10 @@ package repository
 
 import (
 	"context"
-	"database/sql"
 	"fmt"
 	"time"
 
+	"github.com/jackc/pgx/v5"
 	"github.com/jackc/pgx/v5/pgxpool"
 	"github.com/patbritton/sojorn-backend/internal/models"
 	"github.com/rs/zerolog/log"
@@ -1094,7 +1094,7 @@ func (r *PostRepository) ToggleReaction(ctx context.Context, postID string, user
 			// Still need to calculate and return counts
 			goto calculate_counts
 		}
-	} else if err != sql.ErrNoRows {
+	} else if err != pgx.ErrNoRows {
 		log.Error().Err(err).Str("postID", postID).Str("userID", userID).Msg("DEBUG: Failed to check existing reaction - unexpected error")
 		return nil, nil, fmt.Errorf("failed to check existing reaction: %w", err)
 	} else {