fix(ui): stop spurious "Blockchain rescan complete" toast after restoring from minimize

While minimized the main loop skips the frame body (SDL_Delay+continue), so App::update() —
which drains the daemon output via outputSince(daemon_output_offset_) — never runs and the
offset isn't advanced. On restore the whole accumulated backlog is parsed in one batch: a
background witness rebuild's progress lines (parsed as a rescan → state_.sync.rescanning=true)
AND its "rebuilt … in Xms" completion (parsed as finished) arrive together and fire
"Blockchain rescan complete" for a scan the user never initiated.

On WINDOW_RESTORED, discard the daemon-output backlog (advance the offset to the current end,
via App::skipDaemonOutputBacklog) before the resumed update parses it — so only new output is
parsed. Genuine user-initiated rescans still surface completion via the getrescaninfo monitor.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/app.cpp

@@ -5047,6 +5047,18 @@ void App::refreshNow()
     invalidateShieldedHistoryScanProgress(true);
 }
 
+void App::skipDaemonOutputBacklog()
+{
+    // While minimized, App::update() is paused, so daemon_output_offset_ is never advanced and a large
+    // backlog of daemon output piles up. Parsing it all at once on restore would replay a background
+    // witness rebuild's progress + completion in a single batch and fire a spurious "Blockchain rescan
+    // complete" toast. Advance the offset to the current end so only NEW (post-restore) output is parsed.
+    // A genuine user-initiated rescan still surfaces completion via the getrescaninfo monitor.
+    if (daemon_controller_ && daemon_controller_->isRunning()) {
+        (void)daemon_controller_->outputSince(daemon_output_offset_);  // advances daemon_output_offset_ to the end
+    }
+}
+
 void App::handlePaymentURI(const std::string& uri)
 {
     auto payment = util::parsePaymentURI(uri);