Size new images relative to the viewport instead of at native size

️: Currently, pasting / uploading a new image onto the canvas has absolute size - meaning that lots of hi-res images will be way bigger than the current zoom level. On multiplayer canvases, this can block others' work, and on singleplayer canvases it's just annoying as you have to zoom all the way out and shrink it down again. We should consider making the pasted image size either capped, or fully relative, to the current viewport size (accounting for zoom).

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Today a pasted, dropped, or uploaded image lands at its native pixel size, so a high-resolution image can be many times larger than the visible area, and the camera zooms out to fit it. On shared boards the oversized image covers other people's work; on single-player boards the user has to zoom out, shrink the image, and zoom back in. The goal is for a new image to land at a size that suits the current view, accounting for zoom, either by capping it to the viewport or by always sizing it relative to the viewport. I'm assuming the image keeps its full resolution and only its initial on-canvas size changes. Earlier requests (#3136, #1773) pushed the other way, asking for native size so screenshots keep a consistent scale, so the chosen rule should account for that.

Open questions

1. Critical: Should new images be capped to the viewport, or always sized relative to it? Awaiting answer.
2. If capped, how much of the viewport should a new image be allowed to fill? Awaiting answer.
3. Should this be the default behavior for SDK users, or an option that tldraw.com turns on? Awaiting answer.
4. Should videos follow the same rule as images? Awaiting answer.
5. Should there be a way to restore a shrunk image to its native size (as requested in #3168)? Awaiting answer.

Confidence: 40%, blocked on a critical question.