Remove ghost-blog and whishper

Neither is used any more: the blog moves to a self-written site, and
whishper needs more compute than this setup has. Ghost also ran Node 18,
which won't get the eMudhra root store fix.

Drops both apps, the blog DNS record, Gatus check and node001 tunnel
entry, their ca-bundle namespaces, and the leftover ExternalSecret for the
old hensen.io blog namespace. Final Velero backups keep the data:
ghost-blog-final-202610220955 until 22 October 2027 and
whisper-final-202610220955 until 20 January 2027.

nix-infra-machine/nodes/node001.nix

@@ -16,7 +16,6 @@ let
     "argocd.rubenhensen.nl"
     "ha.rubenhensen.nl"
     "longhorn.rubenhensen.nl"
-    "blog.rubenhensen.nl"
     "serpbear.rubenhensen.nl"
     "git.rubenhensen.nl"
     "vic.rubenhensen.nl"