docs(devbox): mark provisioning_tier as an alpha feature

Note that provisioning_tier is alpha and its behavior may change without notice.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: claude

src/resources/shared.ts

@@ -285,8 +285,8 @@ export interface LaunchParameters {
   network_policy_id?: string | null;
 
   /**
-   * (Optional) standard is default and flex is lazily provisioned and may be
-   * pre-empted.
+   * (Alpha) standard is default and flex is lazily provisioned and may be pre-empted.
+   * This is an alpha feature and its behavior may change without notice.
    */
   provisioning_tier?: 'standard' | 'flex' | null;