ui: tighten the badge/dock/tour probes after review and fix the tour's stale hole

The session old-file probe and save_scheduled now discriminate, Esc is read through the real key path, the dock-section probe proves the Measure section starts out of view, and the tour's spotlight is measured independently of the helper it is drawn from. A target scrolled out of its scroller no longer leaves the previous hole standing.

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

src/source_dialog.cpp

@@ -922,8 +922,8 @@ void chooser_tour_mark_seen() {
 void chooser_tour_begin(Chooser& c) {
   if (c.tour.card == nullptr) return;
   chooser_tour_mark_seen();
-  // The chooser's own stack, so a stop can name the page it stands on (the window does the same with
-  // its sidebar in `start_tour()`).
+  // The chooser's own stack, so a stop can name the page it stands on (the window has no stack:
+  // `start_tour()` hooks its slide-over pages in through `on_page`).
   c.tour.page_stack = c.page_stack;
   // The whole table, in walk order: `tour_begin()` drops the stops whose surface is not on screen.
   std::vector<ui_impl::TourStop> stops;