fix: increase fallback detection threshold from 180s to 300s

Pipeline with 3 articles + GPT-5 Image generation legitimately takes
3-4 minutes. The 180-second fallback was triggering before the pipeline
finished, incorrectly reporting "no content" when it was still running.
Increase to 300 seconds to give the pipeline room to complete.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

includes/class-executor.php

@@ -232,8 +232,10 @@ class PRAutoBlogger_Executor {
 				return;
 			}
 
-			// After 3 minutes, check if pipeline produced output despite the kill.
-			if ( $elapsed > 180 ) {
+			// After 5 minutes, check if pipeline produced output despite the kill.
+			// Pipeline with 3 articles + images legitimately takes 3–4 minutes,
+			// so we wait 5 minutes before declaring it orphaned.
+			if ( $elapsed > 300 ) {
 				$recent = get_posts( [
 					'post_type'      => 'post',
 					'post_status'    => [ 'publish', 'draft' ],