Add max-width and max-height caps for LTML widgets

[rowland]

Summary

• Add max-width and max-height support to LTML dimensions and widget APIs with compact in-struct storage.
• Fit <image>, <svg>, and <draw> content inside caps while preserving aspect ratio.
• Surface page overflow no-progress cases as explicit layout errors instead of failing silently.
• Update LTML docs, tests, and affected sample goldens.

Testing

• Added unit coverage for max-dimension parsing, setters, and layout resolution.
• Added regression tests for capped image, SVG, and canvas placement, plus table overflow behavior.
• Ran go test ./ltml and go test ./...; both passed. Sampling was also regenerated to confirm the new rendering behavior.