perf: batch panel resize reads/writes, debounce mastery-slider prefs saves

[carochacs]

Summary

Two verified performance fixes, no behavior change:

1. Layout thrashing in panel resize — sizeCanvases() and the two window-resize handlers that mirror its shape looped over panels doing a getBoundingClientRect()/offsetHeight read immediately followed by canvas style/width/height writes, then read again for the next panel — forcing a synchronous layout recalc every iteration (worst on tri/quad/five/six layouts, up to 6 panels). hw.resize() now takes an optional precomputed {rect, barH}, and the resize call sites measure every panel first, then apply all writes in a second pass — one layout flush instead of N.
2. Un-debounced localStorage write on slider drag — the mastery slider's oninput called savePanelPrefs() on every tick during a drag, which stringifies prefs for every panel (calling hw.getInverted()/getLefty()/getMastery() etc.) and writes to localStorage — potentially dozens of times per drag. Added savePanelPrefsDebounced() (300ms coalescing); the slider handler now uses it. savePanelPrefs() itself cancels any pending debounce timer so every existing direct call site (including stopSplitScreen's teardown-time save) still wins and flushes immediately, avoiding a stale debounced write clobbering splitscreenPanelPrefs after teardown.

Also audited (per CLAUDE.md's documented behavior) and confirmed already correct, no change needed: the popup/LAN time broadcaster's popups.size === 0 && !_lanShare gate, and startTimeSync's 60fps loop (no redundant DOM queries inside it).

Bumped plugin.json version 1.14.2 → 1.14.3 (patch), matching this repo's established convention.

Testing

• node -c screen.js — clean
• node tests/screen.test.js — 33/33 passing, before and after

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[pullfrog]

✅ No new issues found.

Reviewed changes — this review covers commit 1eb1096 against main.

• Layout-thrashing elimination in sizeCanvases() — the main-window resize path now batches every panel's getBoundingClientRect()/offsetHeight reads into a measured array before any canvas-size writes, collapsing N forced layout flushes into one. hw.resize() accepts an optional precomputed {rect, barH} and falls back to self-measuring for single-panel callers.
• Same batching in follower window resize handler — the buildFollowerLayout resize listener mirrors the pattern for multi-panel popups.
• Debounced mastery-slider prefs save — savePanelPrefsDebounced() (300 ms coalescing) replaces the per-tick savePanelPrefs() in the slider's oninput. savePanelPrefs() itself clears any pending debounce timer, so teardown-time saves and every other direct call site still flush immediately without risk of a stale write clobbering state.
• Plugin version bump — 1.14.2 → 1.14.3 patch.

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