Add a GCP GKE Agent Sandbox runtime adapter

[ssalih1993]

Summary

Add a provider-native GCP runtime path for QM:

• provision isolated agent computers through GKE Agent Sandbox SandboxClaim resources
• route the existing agent-daemon protocol through the in-cluster sandbox router
• store durable file bytes and transfer blobs in Cloud Storage
• allow hosted-app deployment to fail closed when no deploy provider is configured
• document the Workload Identity, namespace RBAC, runtime variables, and operator-owned infrastructure boundary

The adapter does not create GKE, Cloud SQL, buckets, IAM, or Secret Manager resources.

Verification

• 37 focused config/GKE/GCS/disabled-provider tests passed
• TypeScript typecheck passed
• ESLint passed on the changed TypeScript files
• diff check passed
• independent review of the GKE control path passed

Live validation

The adapter has been exercised against a GKE Agent Sandbox warm pool. The final compatibility fix uses the request-object API required by @kubernetes/client-node 1.4 for custom resource create/get/delete calls.

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[ssalih1993]

Updated the GKE adapter after validating against a live managed Agent Sandbox CRD. The served v1alpha1 SandboxClaim schema requires spec.sandboxTemplateRef; the equivalent claim passed server-side dry-run. This replaces the rejected warm-pool-specific claim fields while preserving the separately managed warm pool that references the same template. Local full tests (928), typecheck, and lint pass.

[ssalih1993]

Live GKE execution exposed a non-root workspace issue after claim provisioning was fixed: managed Agent Sandbox mounts /home/agent writable to uid/gid 1000, but preserves the image-baked /home/agent/workspace as root-owned 0755. Updated the GKE adapter to create /home/agent/qm-workspace at runtime, avoiding an init container or privilege escalation. Manual live write probe and focused adapter tests pass.