* naming tweaks
* do not mark local element as duplicate when there's no remote counterpart
* merge instead of overwrite elements when saving to firebase & reconcile local state
* decouple syncing from persistence
* fix ts
* clarify doc
* fix reconciliation not removing duplicates
* fix: image not initialized correctly due to not renewing `state.pendingImageElement`
* ensure we replace elements on update
* set file as errored on >= 400 status respones
* feat: support exporting json to excalidraw plus
* add Firebase Storage rules to codebase
* factor the onClick handler out
* move excal icon to icons.tsx
* handle export error