The canvas size was dynamic based on the container div's size. When the div was hidden (e.g. when selecting another tab), the container's effective size is 0. This resulted in the preview image canvas being drawn at a scale of 0.
Fixed by using an absolute size for the canvas container.
- Add lock toggle
- Tweak lock and enabled styles
- Update entity list action bar w/ delete & delete all
- Move add layer menu to action bar
- Adjust opacity slider style
I learned that the inline selector syntax recreates the selector function on every render:
```ts
const val = useAppSelector((s) => s.slice.val)
```
Not good! Better is to create a selector outside the function and use it. Doing that for all selectors now, most of the way through now. Feels snappier.
Previously, canvas actions specific to an entity type only needed the id of that entity type. This allowed you to pass in the id of an entity of the wrong type.
All actions for a specific entity now take a full entity identifier, and the entity identifier type can be narrowed.
`selectEntity` and `selectEntityOrThrow` now need a full entity identifier, and narrow their return values to a specific entity type _if_ the entity identifier is narrowed.
The types for canvas entities are updated with optional type parameters for this purpose.
All reducers, actions and components have been updated.
- create a context for entity identifiers, massively simplifying UI for each entity int he list
- consolidate common redux actions
- remove now-unused code
