fix(highway): a SUPERSEDED renderer init is not a FAILED one (#970)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init() and rejects the previous one with "superseded"; highway.js only checked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    renderer async init failure: Error: superseded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Tests: the superseded guard, and that the throttle opt-out covers both motion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.

static/highway.js

@@ -986,6 +986,22 @@ function createHighway() {
                 // inline arrow function.
                 function _handleAsyncInitFailure(e) {
                     if (hwState._renderer !== _installedRenderer) return;
+                    // ...and ignore a rejection from a SUPERSEDED init cycle.
+                    //
+                    // A renderer mints a fresh readyPromise on every init(), and
+                    // rejects the previous one ("superseded") when a newer init
+                    // starts. The renderer object is unchanged, so the identity
+                    // check above does not catch it — and we would tear down a
+                    // perfectly healthy renderer that is merely re-initialising.
+                    //
+                    // This is exactly what starting a gig did: setViz('venue')
+                    // installed the 3D renderer, then the queue's playSong()
+                    // re-initialised it a tick later; init #1's promise rejected,
+                    // and the gig dropped to the fallback 2D highway with the
+                    // venue gone. A superseded init is not a failed init — the
+                    // NEW cycle owns the outcome, and its own promise is what we
+                    // must judge.
+                    if (_installedRenderer.readyPromise !== rp) return;
                     console.error('renderer async init failure:', e);
                     _destroyCurrentIfInited();
                     hwState._renderer = _defaultRenderer;