Cline SDK 0.0.68: real provider error messages, getShellArgs deprecated

Provider errors forwarded through the Vercel AI Gateway now surface the actual upstream message instead of a Zod dump, and Windows PowerShell commands travel over UTF-8 stdin. SDK consumers should note `getShellArgs()` is deprecated in favour of `getShellInvocation()`.

Tool: cline · Version: sdk/sdk/v0.0.68 · Significance: 2/5 · fix, api-change, deprecation