Post-review deferred items (from #9/#11 review)

[snese]

Deferred non-blocking findings from the #9/#11 review, batched:

• SandboxTemplate hardcodes the gvisor toleration — parameterize the
  tier-owned scheduling fields (toleration + nodeSelector) from
  sandbox.runtimeClassName per the ADR-0007 extension contract, with a
  rendered-fixture test proving a values-only new tier schedules correctly
• Conformance script: run in a dedicated conformance-${RUN_ID} namespace
  with run-scoped PVC names + cleanup trap; add a gVisor × NetworkPolicy
  combined probe (allowed 443 + denied non-443 under the gvisor RuntimeClass)
• Amazon VPC CNI add-on: select an explicitly supported version for the
  declared EKS version and document the upgrade procedure (currently floats)
• Fix EKS version drift in comments (1.34 → 1.35)
• Evaluate NETWORK_POLICY_ENFORCING_MODE=strict with enumerated
  startup flows and rollback criteria (ADR-0008 startup-window caveat)