fix: add electrs-ui to ISO build and first-boot for flawless installs

- Add electrs-ui to ISO capture patterns (captured from live server)
- Bundle nginx:alpine base image in ISO for UI container builds
- Copy docker UI source files (bitcoin-ui, lnd-ui, electrs-ui) into ISO
- First-boot: create electrs-ui container from pre-built image or source
- First-boot: create bitcoin-ui and lnd-ui containers (same pattern)
- Installer: copy docker/ source dir to target for first-boot fallback
- Nginx: minor config sync from linter changes

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

image-recipe/configs/nginx-archipelago.conf

@@ -63,6 +63,7 @@ server {
         proxy_set_header X-Real-IP $remote_addr;
         proxy_buffering off;
         proxy_cache off;
+        proxy_connect_timeout 120s;
         proxy_read_timeout 300s;
         proxy_set_header Connection "";
     }
@@ -441,6 +442,7 @@ server {
         proxy_set_header X-Real-IP $remote_addr;
         proxy_buffering off;
         proxy_cache off;
+        proxy_connect_timeout 120s;
         proxy_read_timeout 300s;
         proxy_set_header Connection "";
     }