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>

docker/bitcoin-ui/Dockerfile

@@ -1,4 +1,4 @@
-FROM 80.71.235.15:3000/archipelago/nginx:1.29.6-alpine
+FROM 80.71.235.15:3000/archipelago/nginx:1.27.4-alpine
 COPY index.html /usr/share/nginx/html/
 COPY 50x.html /usr/share/nginx/html/
 COPY assets/ /usr/share/nginx/html/assets/

docker/electrs-ui/Dockerfile

@@ -1,4 +1,4 @@
-FROM 80.71.235.15:3000/archipelago/nginx:1.29.6-alpine
+FROM 80.71.235.15:3000/archipelago/nginx:1.27.4-alpine
 COPY index.html /usr/share/nginx/html/
 COPY 50x.html /usr/share/nginx/html/
 COPY assets/ /usr/share/nginx/html/assets/

docker/lnd-ui/Dockerfile

@@ -1,4 +1,4 @@
-FROM 80.71.235.15:3000/archipelago/nginx:1.29.6-alpine
+FROM 80.71.235.15:3000/archipelago/nginx:1.27.4-alpine
 
 # Copy the HTML file
 COPY index.html /usr/share/nginx/html/