feat: simplify setup link API and TypeScript SDK

[alongubkin]

Summary

• make setup-link targeting explicit while preserving the existing setup-link request fields
• add idempotent setup-link creation and direct entry points for gateway providers
• simplify TypeScript SDK request inputs so operation bodies are passed directly and workspace can come from the API key
• capture bounded provider error responses for internal diagnostics while keeping gateway responses sanitized
• regenerate the Platform TypeScript SDK from the updated OpenAPI contract

Validation

• AI Gateway unit tests pass (90 tests)
• TypeScript SDK was regenerated from the source OpenAPI schema
• real-provider failure path verified: the upstream 400 body is captured internally while the caller receives the sanitized gateway error

Merge order

Merge this PR before the corresponding Platform PR, which consumes the new AI usage diagnostic fields.

[greptile-apps]

Too many files changed for review (1224 files, 100 file limit).

[alongubkin]

@greptile