fix(oauth): request offline_access for Vercel MCP

[nidhi-singh02]

Summary

• request Vercel's offline_access lifecycle scope during dynamic client registration and authorization so MCP connections receive renewable credentials
• scope the exception to the official https://vercel.com/oauth/authorize endpoint
• add regression coverage for registration and authorization, plus an SDK patch changeset

Linked issue

Fixes #1950

Verification

• bun run format:check
• bun run lint
• bun run typecheck
• TURBO_TEST_CONCURRENCY=2 bun run test (39/39 tasks passed)
• Live self-host verification — reconnect stored a refresh-token pointer and offline_access; Vercel reported healthy with 37 tools

Checklist

• Added a changeset for the published SDK change.
• Added regression tests for the changed OAuth behavior.
• Confirmed no secrets or private deployment details are included.