perf: a frozen frame is not re-rendered sixty times a second

The tick queued a GL render unconditionally. In `Held` and `Paused` the rows
are bound to an immutable snapshot on a pinned axis, so a frame in which none
of the picture's own terms moved is the same frame again. The gate keys on a
coarse signature of what a frozen view can be re-framed by, opens for
`kSettleRenders` frames on a change because the figure lays out per render, and
has a floor that renders anyway every few ticks. The layout editor is excluded:
its buttons are placed from the last frame's rects, so a skipped frame there is
a stale widget rather than a stale picture. `skips=` in the probe dump is the
reading.

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

src/ui_probe.cpp

@@ -2030,11 +2030,16 @@ void pause_probe_report(App& a, const char* what) {
   // The bar's own string, because "how long have I been paused" is a *status* field and the
   // elapsed figure is the one part of it that no other line can show: the exit dump's
   // `status bar:` is read live and the two `mode ...` lines are the live and triggered states.
+  // `skips` is the render gate (see the end of `tick()`), cumulative over the session: it must be
+  // 0 on the `live` report and have grown by the `paused` one, which is the gate being a number
+  // rather than a claim. A live view that skips frames is the gate's condition inverted; a paused
+  // view that skips none is the gate not engaging at all.
   std::fprintf(stderr,
                "[pause-probe] %-9s paused=%d ring_produced=%zu event_size=%zu "
-               "frozen_x=[%.6f..%.6f] axis=[%.6f..%.6f] glance=[%s]\n",
+               "frozen_x=[%.6f..%.6f] axis=[%.6f..%.6f] skips=%d glance=[%s]\n",
                what, a.model->paused() ? 1 : 0, ring_produced, event_size, bounds_lo, bounds_hi,
-               double(axis.min), double(axis.max), a.dbg_glance_last.c_str());
+               double(axis.min), double(axis.max), a.dbg_render_skips,
+               a.dbg_glance_last.c_str());
   std::fflush(stderr);
 }