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.

dankserver/romm/quadlet/romm-mariadb.container

@@ -14,7 +14,7 @@ After=network.target
 
 [Container]
 ContainerName=romm-mariadb
-Image=docker.io/library/mariadb:11
+Image=docker.io/library/mariadb:11@sha256:f16d7a344413e519dff518f27bdb221388f84b0d274c97c4fb5f2cb0dc1b34fa
 Network=dankserver_appnet:alias=mariadb
 EnvironmentFile=/home/dank/Containers/romm/env
 Environment=MARIADB_DATABASE=romm