fix: container stack installers, DNS resolution, uninstall cleanup

- Replace aardvark-dns container names with host.containers.internal
  for all cross-app connections (LND→Bitcoin, ElectrumX→Bitcoin,
  Mempool→ElectrumX, Fedimint→Bitcoin, NBXplorer→Bitcoin P2P+RPC)
- Add BTCPay multi-container stack installer (postgres + nbxplorer +
  btcpay-server) with proper secrets, data dir ownership, NOAUTH
- Add Mempool multi-container stack installer (mariadb + mempool-api +
  mempool-frontend) with host.containers.internal for RPC
- Immediately remove apps from state on uninstall (no 3-min ghost delay)
- Include archy-bitcoin-ui in bitcoin uninstall container list
- Fix LND UI port 8081 (was 8080, conflicting with LND gRPC)
- Fix ElectrumX UI: proxy /electrs-status to backend, cache-busting
  headers, graceful fallback when backend returns HTML
- Add Tor hidden services for ElectrumX and LND in torrc template
- Remove unused detect_bitcoin_container_name() (replaced by
  host.containers.internal)

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

docker/lnd-ui/nginx.conf

@@ -1,5 +1,5 @@
 server {
-    listen 8080;
+    listen 8081;
     server_name _;
 
     root /usr/share/nginx/html;