perf: allocation/scan hardening for weaker hardware

Static-analysis follow-ups to the trace-backed fixes; each is cheap
insurance on machines where the profiled headroom doesn't exist.

- highway.js: _makeBundle now mutates one persistent per-instance
  object instead of allocating a fresh ~35-field bundle every rAF
  frame (xN under splitscreen). Object identity is stable and
  meaningless; array fields still swap reference on chart changes,
  which field-identity caches rely on. Contract documented in both
  CLAUDE.mds.
- highway.js: new bsearchTime (lower-bound on .time) windows the
  default 2D renderer's beat-line scan (was O(all beats) per frame);
  bundle.lowerBoundT / bundle.lowerBoundTime expose the searches to
  custom viz so they stop reimplementing visible-window culling.
- highway_3d: localStorage 'h3d_full_sus' polled at ~1 Hz instead of
  every frame (synchronous storage read on the hot path).
- highway_3d: drawLyrics caches the measureText row layout keyed on
  (lyrics ref, line index, shown count, font size, width) — per-frame
  work is now just drawing over cached widths.
- tests/js: bundle source-shape assertions widened to accept the
  assignment form ([:=]) alongside the old object-literal form.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/js/highway_adaptive_scale.test.js

@@ -82,7 +82,7 @@ test('draw() only adapts during active playback and feeds the HUD', () => {
 
 test('bundle + canvas sizing use the effective scale, not the raw user value', () => {
     const src = fs.readFileSync(highwayJs, 'utf8');
-    assert.match(src, /renderScale:\s*_effectiveRenderScale\(\)/, 'bundle.renderScale must be the effective scale');
+    assert.match(src, /renderScale\s*[:=]\s*_effectiveRenderScale\(\)/, 'bundle.renderScale must be the effective scale');
     assert.match(src, /canvas\.width\s*=\s*Math\.round\(w\s*\*\s*_effectiveRenderScale\(\)\)/, 'canvas backing store must use effective scale');
 });