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

dankserver/romm/quadlet/romm-redis.container

@@ -12,7 +12,7 @@ After=network.target
 
 [Container]
 ContainerName=romm-redis
-Image=docker.io/library/redis:7-alpine
+Image=docker.io/library/redis:7-alpine@sha256:858f009f9709ce576febc734aa78b8f6d624b82571f9ddb6bda4377c833b3499
 Network=dankserver_appnet:alias=redis
 Volume=/home/dank/Containers/romm/redis:/data
 HealthCmd=redis-cli ping

dankserver/romm/quadlet/romm.container

@@ -18,7 +18,7 @@ After=romm-mariadb.service romm-redis.service network.target
 
 [Container]
 ContainerName=romm
-Image=ghcr.io/rommapp/romm:latest
+Image=ghcr.io/rommapp/romm:latest@sha256:03295f95a6290e752641f9553ac4198b0e5b71b879d57f7b2371b98f608feb54
 Network=dankserver_appnet
 EnvironmentFile=/home/dank/Containers/romm/env
 Environment=DB_HOST=mariadb