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.

tests/seerr_quadlet.bats

@@ -20,8 +20,9 @@ SEERR_UNIT="$REPO_ROOT/dankclaw/seerr/quadlet/seerr.container"
     grep -q '^Restart=always$' "$SEERR_UNIT"
 }
 
-@test "seerr image is pinned to an exact version tag" {
-    grep -Eq '^Image=ghcr\.io/seerr-team/seerr:v[0-9]+\.[0-9]+\.[0-9]+$' "$SEERR_UNIT"
+@test "seerr image is pinned to an exact version tag and digest" {
+    # 2026-10-21 fleet law: tag AND digest (tests/quadlet_image_pins.bats)
+    grep -Eq '^Image=ghcr\.io/seerr-team/seerr:v[0-9]+\.[0-9]+\.[0-9]+@sha256:[0-9a-f]{64}$' "$SEERR_UNIT"
 }
 
 @test "seerr publishes 5055 on loopback only (guard chain is the user path)" {