fix(daemon): make the "keep the node running?" prompt actually appear

Quitting during a witness rebuild is supposed to ask before stopping the
node, because a stop throws the rebuild away and a killed node replays
and redoes it. The guard almost never fired:
- it returned false for any daemon >= v1.3.0, on the false premise that
  v1.3.0 checkpoints a rebuild (it does not; nothing survives a kill)
- it read a 16 KB debug.log tail and compared the last progress line with
  the newest line, so any unrelated line during the rebuild's silent
  second phase turned it off; and on POSIX that file is stale
- daemon_version, which the bypass needed, is zeroed when a busy node
  drops the connection

Now a DaemonBusyTracker (src/daemon/daemon_busy_detect.h, pure) follows
dragonxd's own markers in order: rebuilding (Phase-1 / legacy markers,
ended by the completion line, an abort line or the next UpdateTip) and
replaying (Activating best chain ... Done Loading), reset by a new banner
or "Shutdown: done". It is fed from the owned output on the UI thread,
including the backlog skipped after a restore. The quit guard prompts
when the quit would stop the node and it is rebuilding, or has been
alive but only timing out / refusing as busy for >= 30 s. A replay alone
never prompts: stopping it is safe. The stop loop uses the same signal
to never offer Kill during a rebuild.

Also:
- daemon output offsets are absolute, so a reader that falls behind a
  trim of the 1 MB buffer no longer skips new output (which could hide a
  start or end marker)
- a quit deferred while minimized restores and raises the window, and
  the wizard renders the prompt, so it is never waiting unseen

Verified live with the fake daemon: quitting mid-rebuild now shows the
prompt for a v1.3.0 node and leaves the node alone; a silent busy node
prompts after 30 s.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/daemon/embedded_daemon.cpp

@@ -267,6 +267,7 @@ void EmbeddedDaemon::appendOutput(const char* data, size_t len)
 {
     // Caller must hold output_mutex_
     process_output_.append(data, len);
+    output_total_ += len;
     if (process_output_.size() > MAX_OUTPUT_BYTES + MAX_OUTPUT_BYTES / 4) {
         // Trim to MAX_OUTPUT_BYTES, cutting at a newline boundary
         size_t trim_to = process_output_.size() - MAX_OUTPUT_BYTES;