Cross-organization artifact asset copying, with new consent gate

Artifacts (Claude Code's generated documents/apps) can copy assets from one artifact into another. This copy action now recognizes when the source artifact belongs to a different organization than the destination, and handles it explicitly:

• Copying from a public artifact outside your organization now shows a specific approval prompt before proceeding.
• Copying from an artifact shared directly from another organization shows a similar, separate approval prompt.
• If the destination artifact belongs to another organization, the copy is refused outright, with a message explaining that assets can only be copied into artifacts in your own organization.
• If the server doesn't yet support cross-organization copying, the tool now gets a distinct error telling it not to retry, instead of failing unclearly.
• Artifacts shared from another organization aren't yet listed automatically, so the user needs to supply the link directly.

This builds on the permission-rule checks already added for artifact copying: a new consent mechanism specifically for cross-organization copies now sits alongside it, so a human must approve before an outside-organization copy proceeds.