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>

CLAUDE.md

@@ -231,6 +231,18 @@ window.feedBackViz_my_viz = function () {
             // toneChanges, toneBase, mastery, hasPhraseData, inverted,
             // lefty, renderScale, lyricsVisible, the 2D coordinate
             // helpers project and fretX, and getNoteState (see below).
+            // The bundle OBJECT is reused across frames (mutated in
+            // place — no per-frame allocation): never cache it or
+            // compare its identity between frames; field values are
+            // only valid for the current draw call. Array FIELDS still
+            // swap reference when chart data changes, so field-identity
+            // caches (`myRef !== bundle.chords`) remain valid.
+            // Windowed-iteration helpers (stable fn refs): bundle
+            // .lowerBoundT(arr, time) is a lower-bound binary search on
+            // `.t` (notes/chords); bundle.lowerBoundTime(arr, time) on
+            // `.time` (beats/anchors/sections). Use these to cull to
+            // the visible window instead of full-scanning chart arrays
+            // per frame.
             // `stringCount` is the active arrangement's string count (4
             // for bass, 6 for guitar, 7+ for extended-range GP imports —
             // size string-indexed geometry against this, not a hardcoded