fix: auto-build UI containers for Bitcoin, LND, Electrumx

Critical: headless services (Bitcoin, LND, Electrumx) need companion
UI containers that serve web dashboards. These were only built for
Bitcoin, and only on bundled ISO builds.

Changes:
- install.rs: auto-build UI containers for LND (port 8081) and
  Electrumx (port 50002) in addition to Bitcoin (port 8334)
- build-auto-installer-iso.sh: always bundle docker UI source files
  (was skipping for unbundled builds — they're tiny HTML, not images)
- Dockerfiles: fix nginx base image tag 1.29.6→1.27.4 (matches registry)

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

image-recipe/build-auto-installer-iso.sh

@@ -1370,9 +1370,9 @@ if [ -f "$SCRIPT_DIR/../scripts/image-versions.sh" ]; then
     echo "   ✅ Bundled image-versions.sh"
 fi
 
-# Bundle docker UI source files for building custom UIs on first boot (fallback if images not captured)
-# Skip for unbundled builds
-if [ "$UNBUNDLED" != "1" ]; then
+# Bundle docker UI source files for building custom UIs on first boot
+# Always bundle — these are tiny HTML/CSS files, not container images
+if true; then
     DOCKER_UI_DIR="$SCRIPT_DIR/../docker"
     if [ -d "$DOCKER_UI_DIR" ]; then
         echo "   Bundling docker UI source files..."