* fix: remove redundant LabelsSubmenu; add readonly prop

* feat: add readonlyToolbar, display instead of leftToolbar

* feat: add Users toolbar in readonly mode

* fix: Users icon fill WIP

* feat: add LayersPopover

* fix: initialize Users autocomplete properly

* fix: react component keys

* fix: Layers icon / tooltip

* fix: lint errors

* fix: initialise users autocomplete with correct username

* fix: lint errors

* fix: remove unused imports

* fix: button popping in readonlyToolbar

* fix: update ui.state.activeAnnotationID on user change

* fix: disable mouse events (except click-select) in readonly mode

* fix: prettier

* feat: add readonly example at localhost:3000/readonly

* fix: switch toolbox on layer switch

* feat: add second annotation to readonly example so users list is populated

* feat: readonly mode Percy test

* refactor: move canvases to CanvasStack component

* feat: pass spline canvas ref to ui using forwardRef

* feat: two CanvasStacks side by side (WIP)

* fix: set position: relative on divs containing position: absolute children

* feat: add DiffCanvas

* fix: recompute diff when input canvas dimensions change

* feat: user2 / annotationsObject2 in ui.tsx

* fix: recompute diff when diffcanvasref updates, show on right side only

* feat: enable PaintbrushCanvas and BoundingBoxCanvas diffs

* fix: use all three annotations canvases in diff

* merge: omit isSuper from PaintbrushCanvas props

* merge: remove select icon in readonly mode

* fix: pointerEvents: "none" in DiffCanvas div

* fix: disable new annotation shortcut in readonly mode

* fix: simplify diff updates

* feat: add diff toggle button

* fix: call drawDiff via setTimeout in ref callback

* feat: single/side-by-side view toggle

* feat: show both annotations in LayersPopover

* fix: don't create empty object for annotationsObject2

* feat: two user selection in UsersPopover

* fix: pass correct value as annotationsObject2 to LayersPopover

* fix: lint errors

* fix: label inputs User 1 and User 2 in UsersPopover

* fix: tooltips

* fix: update style

* fix: redrawEverything on diff toggle

* feat: dividing line in sidebyside mode

* feat: username boxes

* fix: disable toolbox warning snackbar in readonly mode

* fix: lint error

* fix: tweak namebox style

* fix: close background toolbar on clickaway

* fix: halve thickness of dividing line

* fix: eliminate 1px gap at top of dividing line

* fix: call redrawEverything in diff toggle setState callback

* fix: pass redrawEverything to DiffCanvas

* fix: lint error

* fix: 10ms delay on drawDiff timeout

* fix: reduce drawDiff delay to 1ms

* fix: 5ms

* fix: 10ms

* fix: lint errors

* fix: abort drawDiff when input canvases are missing

* fix: make new annotations in empty annotationsObjects

* fix: only show diffToolbar in comparison mode

* fix: bump @mui/material

* fix: rename readonly test

* fix: hard-code TARGET_URL for readonly test

* fix: append /readonly to TARGET_URL

* fix: redirect unhandled http-server requests to homepage