feat(security): digest-pin every registry image on all three hosts (fleet law)

Closing the command-center security queue #70/#71/#72/#73/#74: rolling tags
let a rebuild move under a running service with nobody approving it, and
make a CVE audit ungradeable. 36 quadlet units across dankclaw, dankserver
and frankbook-pro now carry tag@sha256; localhost/* builds stay exempt
(their build is the pin). The pihole and copyparty pins pull the fixed
builds; valkey 9.1.2 (already running) and redis 7.4.11 are pinned in
place, vendor fixes TBD.

New gate tests/quadlet_image_pins.bats: no unpinned registry image, no
generator-rejected key anywhere. Three seams that pinned the old exact-tag
law (frankbook readarr, open_webui, seerr) now require tag AND digest -
strictly stronger. Quadlet Lifecycle docs: batch-abort law, entrypoint
flags-only law, pin law.

frankbook-pro/prowlarr/quadlet/prowlarr.container

@@ -24,7 +24,7 @@ After=gluetun.service
 
 [Container]
 ContainerName=prowlarr
-Image=lscr.io/linuxserver/prowlarr:latest
+Image=lscr.io/linuxserver/prowlarr:latest@sha256:b3b00047ed20f6ce2b16780145cb6a0acb51c9e28ea6aa6f5dcd33c7034f1797
 Environment=PUID=0
 Environment=PGID=0
 Environment=TZ=America/Los_Angeles