[codex] Add node reinstall command

[NitayRabi]

What changed

• add a first-class reinstall command to the shared amesh and amesh-node CLIs
• teach the installer a destructive reinstall mode that removes stale node service, state, config, binaries, and managed amesh home before reinstalling
• document the supported recovery flow and add reinstall-specific Go and shell regression coverage

Why

When a node install gets into a bad state, the only recovery path was manual file cleanup. That made it harder to distinguish stale reconnect state from stale detected agent config or stale managed ACPX/runtime wiring.

Impact

• operators can now run amesh reinstall or amesh-node reinstall for a supported from-scratch node recovery
• reinstall preserves the user's ACPX config while rebuilding amesh-managed node artifacts from scratch
• the recovery flow is covered by both CLI-level and installer-level regression tests

Validation

• go test ./...
• bash scripts/test-install-amesh-node.sh

[NitayRabi]

Closing this stacked draft in favor of a clean PR targeted directly at main.