- Add IS_BROWSER constant to core/constants.ts, rewrite IS_TAURI to use it
- Replace 9 raw 'typeof window' checks across canvaskit, fig-export,
figma-api, fig-file, fonts, SafariBanner, use-chat
- Promote no-typeof-window-check lint rule from warn to error
- Extract array mutation helpers (updateArrayItem, removeArrayItem,
toggleArrayVisibility) into useMultiProps — DRY up FillSection and
StrokeSection (removes 20+ duplicated for-loops)