fix(highway): a SUPERSEDED renderer init is not a FAILED one (#970)

Starting a gig dropped the player onto the fallback 2D highway with no venue.

startGig() calls setViz('venue'), which installs the 3D renderer — whose init is
async — and then immediately starts its play queue. playSong() re-initialises
that same renderer a tick later. A renderer mints a fresh readyPromise per
init() and rejects the previous one with "superseded"; highway.js only checked
that the RENDERER OBJECT was unchanged, which it is. So it treated a healthy,
re-initialising renderer as a failed one, tore it down, and reverted to 2D:

    renderer async init failure: Error: superseded
    viz picker: reverted to default renderer (async-init-failure)

The guard now also checks the PROMISE identity: a rejection from an init cycle
the renderer has already moved on from is ignored. The renderer-identity guard
stays (a rejection for a renderer since REPLACED is also not ours), and a
genuine failure of the CURRENT cycle still reverts — both init() call sites go
through _setRenderer, which re-wires the handler every time, so the new cycle is
always watched.

Reproduced and fixed against the real build:

    before:  vizSelection=default  viz-picker=default  venue=inactive  viz:reverted
    after:   vizSelection=venue    viz-picker=venue    venue=ACTIVE    (no revert)

Also widens the paused-frame throttle's opt-out. The throttle fires whenever the
CHART CLOCK is stalled — not only on a pause, but through a count-in and the
credits/author overlay too. Its opt-out only asked "is a crowd video rolling",
but the venue scene animates on a clock of its own with no pack at all (backdrop
breathe, parallax, haze drift, warmth pulse — Math.sin(t) in the draw loop), so
that motion was still being throttled. It now claims frames for both sources; a
plain 3D highway with no venue reads motion mode 'off' and keeps the #654 GPU
saving.

HONEST CAVEAT on that second part: I could not get the throttle to fire in a
reproduction. A control run on the shipped code showed 100 draws/sec while
paused, not the ~10/sec a firing throttle would give — so the change is
defensible on its own terms (a stalled clock is genuinely not a static picture)
but it does NOT have a demonstrated symptom behind it. The viz fix above does.

Tests: the superseded guard, and that the throttle opt-out covers both motion
sources. All fail against the pre-fix source. eslint 0 errors; JS 1207/1207.

plugins/highway_3d/screen.js

@@ -15398,15 +15398,29 @@
             // highway throttled the whole room. Pausing the song dropped the
             // venue, the crowd and the stage to 10 fps.
             //
-            // Only claim continuous frames while a crowd video is actually
-            // rolling: with no venue pack (the common case) the paused scene IS
-            // static and the throttle should still save the GPU.
+            // Two independent sources of motion, and BOTH must keep their frames:
+            //
+            //  • a crowd video rolling on its own clock (career venue pack), and
+            //  • the venue scene's own fake-depth motion — the backdrop breathes,
+            //    the haze drifts, warmth pulses, the shimmer moves. That is
+            //    Math.sin(t) in the draw loop (see _venueApplyFakeDepthMotion),
+            //    so it only moves while we are actually given frames, and it runs
+            //    with NO pack at all.
+            //
+            // The throttle fires whenever the CHART CLOCK is stalled — which is
+            // not just a pause. A count-in and the credits/author overlay stall it
+            // exactly the same way, so the venue was stuttering there too.
+            //
+            // With no venue at all (plain 3D highway) the paused scene really is a
+            // still picture: motion mode reads 'off', we claim nothing, and the
+            // throttle still saves the GPU as #654 intended.
             needsContinuousFrames() {
                 if (!_isReady || _ctxLost) return false;
                 for (const v of _venueCrowdVideos) {
                     if (v && !v.paused && !v.ended && v.readyState >= 2) return true;
                 }
-                return false;
+                // 'off' also covers prefers-reduced-motion and "no venue scene".
+                try { return _venueEffectiveMotionMode() !== 'off'; } catch (_) { return false; }
             },
 
             draw(bundle) {