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/jellyfin/quadlet/jellyfin.container

@@ -16,7 +16,7 @@ After=network.target
 
 [Container]
 ContainerName=jellyfin
-Image=ghcr.io/jellyfin/jellyfin:latest
+Image=ghcr.io/jellyfin/jellyfin:latest@sha256:c3efa69a22f2691fc88d6bb035e87a8560e395a6047f062fb381c61c3185e8f5
 Network=dankserver_appnet
 Environment=DEBIAN_FRONTEND=noninteractive
 Environment=DOTNET_SYSTEM_IO_DISABLEFILELOCKING=true