fix(lightning): channel open raced async peer connect, errors were swallowed

- Connect to peer synchronously (perm=false, 30s timeout) and check the
  result before opening the channel; previously the connect was fired
  with perm=true (queued in background, returns immediately) and its
  result ignored, so the open failed with 'peer is not online'
- Let LND channel/peer errors through the error sanitizer so the UI
  shows the real cause instead of 'Check server logs'
- Add private (unannounced) channel option to backend and UI — some
  peers (e.g. Olympus/ZEUS LSP) reject public channel opens

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

core/archipelago/src/api/rpc/middleware.rs

@@ -61,6 +61,9 @@ pub(super) fn sanitize_error_message(msg: &str) -> String {
         "Session",
         "Failed to pull",
         "Failed to start",
+        "Failed to open channel",
+        "Failed to close channel",
+        "Failed to connect to peer",
         "Container",
         "Image",
         "Bitcoin address",