fix: reduce memory_limit to 256M and configure PHP-FPM process management settings

docker/php/zz-pool.conf

@@ -5,3 +5,14 @@
 ; wrong environment. Keep the container env so compose-provided vars reach PHP.
 [www]
 clear_env = no
+
+; Process manager: bounded pool + child recycling. Without pm.max_requests the
+; default children live forever and slow PHP memory leaks accumulate for hours
+; until the host OOMs (the messenger workers already recycle hourly; this gives
+; FPM the same hygiene).
+pm = dynamic
+pm.max_children = 8
+pm.start_servers = 2
+pm.min_spare_servers = 2
+pm.max_spare_servers = 4
+pm.max_requests = 500