Fixed the CI failures in packages/opencode/src/server/routes/instance/httpapi/event.ts.

The failing SDK instance event stream test was hitting a lazy bus.subscribeAll() after the request middleware instance context had already unwound. I changed the instance SSE handler to subscribe while still inside the handler/request context, forward bus events through a Queue, and clean up by unsubscribing/shutting down the queue when the stream closes.

Verified locally after merging latest dev:

• bun test --timeout 30000 test/server/httpapi-sdk.test.ts -t "matches generated SDK instance event stream"
• bun test --timeout 30000 test/server/worktree-endpoint-repro.test.ts
• bun test --timeout 30000 test/server/httpapi-cors.test.ts -t "uses custom CORS origins passed to the server"

Also passed bun turbo typecheck during push.