fix(provider/anthropic): correct Claude 4 model ID format

[mmstroik]

Background

Anthropic's official Claude 4 model IDs use the format claude-opus-4-20250514 and claude-sonnet-4-20250514, but the AI SDK was using the format claude-4-opus-20250514 and claude-4-sonnet-20250514.

Summary

Updated Claude 4 model ID to match Anthropic's official format:

• claude-4-opus-20250514 --> claude-opus-4-20250514
• claude-4-sonnet-20250514 --> claude-sonnet-4-20250514

Changes made to:

• TypeScript model ID types in anthropic provider (AnthropicMessagesModelId type)
• Provider documentation
• Cookbook examples
• Model reference tables
• Migration guide examples

Verification

Verified against Anthropic's official documentation that the correct model IDs are claude-opus-4-20250514 and claude-sonnet-4-20250514.

Tasks

• Documentation has been added / updated (for bug fixes / features)
• A patch changeset for relevant packages has been added (for bug fixes / features - run pnpm changeset in the project root)
• Formatting issues have been fixed (run pnpm prettier-fix in the project root)

Future Work

I didn't change the AI Gateway model ids since those are obviously vercel-specific ids that are routed internally, but note that those also use the older format (claude-4-sonnet rather than claude-sonnet-4)