fix(copilot): use copilot key for provider options

The new copilot provider looks for providerOptions.copilot, not
providerOptions.openaiCompatible. This ensures that custom options
are passed through.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: SteffenDE

packages/opencode/src/provider/transform.ts

@@ -20,6 +20,7 @@ export namespace ProviderTransform {
   function sdkKey(npm: string): string | undefined {
     switch (npm) {
       case "@ai-sdk/github-copilot":
+        return "copilot"
       case "@ai-sdk/openai":
       case "@ai-sdk/azure":
         return "openai"