refactor: create shared script library, fix ISO image pinning, document planned splits

- S21: Create scripts/lib/common.sh with shared logging, SSH, health check, mem_limit functions
- S18: Source common.sh from deploy-to-target.sh, deploy-tailscale.sh, first-boot-containers.sh
- S16: Fix 2 hardcoded images in ISO build, add missing image variables
- S19: Document planned 7-module split of build-auto-installer-iso.sh
- S20: Document planned 8-module split of first-boot-containers.sh

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/image-versions.sh

@@ -46,6 +46,8 @@ FEDIMINT_GATEWAY_IMAGE="docker.io/fedimint/gatewayd:v0.5.1"
 
 # Media
 IMMICH_IMAGE="ghcr.io/immich-app/immich-server:v1.123.0"
+IMMICH_POSTGRES_IMAGE="ghcr.io/immich-app/postgres:14-vectorchord0.4.3-pgvectors0.2.0"
+IMMICH_VALKEY_IMAGE="docker.io/valkey/valkey:7-alpine"
 REDIS_IMAGE="docker.io/library/redis:7"
 
 # Penpot
@@ -63,5 +65,11 @@ MINIO_IMAGE="docker.io/minio/minio:RELEASE.2024-11-07T00-52-20Z"
 INDEEDHUB_POSTGRES_IMAGE="docker.io/library/postgres:16-alpine"
 INDEEDHUB_REDIS_IMAGE="docker.io/library/redis:7-alpine"
 
+# DWN (Decentralized Web Node)
+DWN_SERVER_IMAGE="ghcr.io/tbd54566975/dwn-server:main"
+
+# Penpot postgres (separate from BTCPay postgres — different version)
+PENPOT_POSTGRES_IMAGE="docker.io/library/postgres:15"
+
 # Base images
 NGINX_ALPINE_IMAGE="docker.io/library/nginx:alpine"