fix: resolve available Ubuntu templates safely

[solomonneas]

Summary

• Resolve the newest available Ubuntu 22.04 Proxmox template instead of assuming one historical archive still exists, then verify the downloaded volume before provisioning.
• Run template resolution once before deployment, fail without component state writes when it cannot succeed, and preserve completed-component reruns unless --force is set.

Verification

• ./scripts/verify: shellcheck, manifest checks, and 142 Bats tests passed. Brigade receipt 20260829-152726-work-verify-28171e.
• Focused template and orchestrator regressions: 11 tests passed. Brigade receipt 20260829-152545-work-verify-d4f66c.

Risk

Template selection remains limited to Ubuntu 22.04 because every current component manifest declares that release family.

Closes #7

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