fix(node): surface why an embedded daemon dies right after spawning

The daemon can spawn successfully (CreateProcess OK) and then exit immediately —
a missing runtime DLL, wrong architecture, corrupt binary, datadir lock, etc.
EmbeddedDaemon's crash monitor already builds a detailed reason for this
(translated Windows exit code, e.g. "STATUS_DLL_NOT_FOUND — required DLL not
found", plus the launch command and a debug.log tail) and stores it in
lastError(), but it runs on a background thread and was never shown. The result
was the exact symptom users reported: the wallet unpacks dragonxd.exe, looks
"stuck connecting", and the node silently dies-and-respawns until it gives up —
with no visible reason (manually starting dragonxd works, so the wallet then
connects to it).

tryConnect now watches the daemon's crash count (on the main thread, where it
already logs daemon state) and surfaces each NEW crash's lastError() once, as a
sticky error notification, with a concise "Couldn't start dragonxd" status. The
counter resets on a successful connect (alongside the daemon's own crash-count
reset), so a later crash re-notifies.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app.h

@@ -511,6 +511,7 @@ private:
     // and show the embedded-daemon start failure (binary/params/spawn) only once. Reset on connect.
     int daemon_wait_attempts_ = 0;
     bool daemon_start_error_shown_ = false;
+    int daemon_last_seen_crashes_ = 0;  // surface each new embedded-daemon crash reason once
     float loading_timer_ = 0.0f;  // spinner animation for loading overlay
 
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