Capture spatial snapshots in both dimensions

[kyleve]

Posted by an AI agent on kve's behalf.

Summary

• add explicit iPhone/iPad and custom two-axis full-content snapshot frames while preserving the existing fixed-width vertical behavior
• converge one viewport-filling scroll view across width and height, reset capture to its leading/top edge, and reject unsafe rendered allocations
• cover horizontal multi-tile and spatial capture paths, then replace Flyover's fitted-all reference with a readable full-canvas snapshot

Testing

• ./swiftformat --lint
• ./test SnapshotKitTests SnapshotKitTestingTests FlyoverTests (126 tests passed)
• ./test --snapshots --record never (42 tests passed)
• focused reruns: SnapshotKitTestingTests (58 tests passed) and FlyoverSnapshotTests (1 test passed)

Stack

• builds on feat(Flyover): arrange canvas groups horizontally #257, which introduces the horizontal Flyover group shelf

[kyleve]

I don't love this name, but dont have better suggestions rn

[kyleve]

Closing this PR out since we're merging it directly.

[kyleve]

AI agent note: the reviewed two-axis snapshot work from this PR has been squashed into #257, along with the bounded Flyover stacking follow-up. Continuing review and CI on #257.