Fix session/image UX and align post cost totals

includes/class-admin-columns.php

@@ -77,16 +77,10 @@ class WP_Agentic_Writer_Admin_Columns {
 			return;
 		}
 
-		global $wpdb;
-		$table_name = $wpdb->prefix . 'wpaw_cost_tracking';
-
-		// Get total cost for this post
-		$total_cost = $wpdb->get_var(
-			$wpdb->prepare(
-				"SELECT SUM(cost) FROM {$table_name} WHERE post_id = %d",
-				$post_id
-			)
-		);
+		$total_cost = 0.0;
+		if ( class_exists( 'WP_Agentic_Writer_Cost_Tracker' ) ) {
+			$total_cost = WP_Agentic_Writer_Cost_Tracker::get_instance()->get_session_total( $post_id );
+		}
 
 		if ( $total_cost && $total_cost > 0 ) {
 			// Color code based on cost