[backups] Fix pg_dump not found in celery backup task

CHANGELOG.org

@@ -1,5 +1,20 @@
 #+title:  CHANGELOG
 
+* Version 65.4 [1/1]
+** DONE [#A] Fix database backup bug where running in celery task fails :bug:backups:celery:tasks:
+:PROPERTIES:
+:ID:       4117482f-4774-49b8-93b2-5b97adb194bd
+:END:
+
+*** Description
+
+The `backup_database` celery task failed with `No such file or directory
+'pg_dump'` even though the manual management command worked. FreeBSD rc.d
+celery workers run under daemon(8) with a minimal PATH that omits
+`/usr/local/bin`. The task now resolves `pg_dump` via `shutil.which()`,
+falling back to the common PostgreSQL install locations, instead of relying
+on the inherited PATH.
+
 * Version 65.3 [1/1]
 ** DONE [#B] Trail scrobbles without names should try to use trial heads loc :trails:metadata:
 :PROPERTIES: