feat: electrs standalone install with bitcoin dependency + progress UI

- Add electrs to marketplace as standalone installable app
- Add dependency check: refuse install if no bitcoin node is running
- Use container DNS (bitcoin-knots:8332) on archy-net instead of host IP
- Auto-create bitcoin.conf with txindex + RPC on bitcoin-knots install
- Auto-build and start electrs-ui container post-install
- Show index size and estimated progress during initial sync
- Add /electrs-status and /health nginx proxy routes
- Remove Tailwind CDN from electrs-ui, use inline styles

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

image-recipe/configs/nginx-archipelago.conf

@@ -107,13 +107,26 @@ server {
         proxy_http_version 1.1;
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
-        
+
         # Increase timeout for long-running operations (e.g., Docker image pulls)
         proxy_connect_timeout 600s;
         proxy_send_timeout 600s;
         proxy_read_timeout 600s;
     }
-    
+
+    # Backend status endpoints (must be before the SPA catch-all)
+    location /health {
+        proxy_pass http://127.0.0.1:5678/health;
+        proxy_http_version 1.1;
+        proxy_set_header Host $host;
+    }
+    location /electrs-status {
+        proxy_pass http://127.0.0.1:5678/electrs-status;
+        proxy_http_version 1.1;
+        proxy_set_header Host $host;
+        add_header Access-Control-Allow-Origin *;
+    }
+
     # Proxy apps that set X-Frame-Options - strip header so iframe works
     location /app/nextcloud/ {
         proxy_pass http://127.0.0.1:8085/;
@@ -462,6 +475,18 @@ server {
         proxy_set_header X-Real-IP $remote_addr;
     }
 
+    location /health {
+        proxy_pass http://127.0.0.1:5678/health;
+        proxy_http_version 1.1;
+        proxy_set_header Host $host;
+    }
+    location /electrs-status {
+        proxy_pass http://127.0.0.1:5678/electrs-status;
+        proxy_http_version 1.1;
+        proxy_set_header Host $host;
+        add_header Access-Control-Allow-Origin *;
+    }
+
     location /rpc/ {
         proxy_pass http://127.0.0.1:5678;
         proxy_http_version 1.1;