[codex] Fix node self-update flow

[NitayRabi]

What changed

• pass the active node server/config/state context into daemon-triggered updates instead of launching the installer with default assumptions
• add self-update installer handling so remote updates do not stop their own systemd service mid-run and can succeed from saved node state without an explicit SERVER_URL
• extend Go and installer regression coverage for the remote update path

Why

Remote node updates were being accepted by the control plane but never completing reliably on the node. The updater depended on installer inputs like SERVER_URL that were not preserved by the managed service, and self-updates could stop their own service before the restart path had a chance to take over.

Impact

• dashboard-triggered node updates now reuse the node's live runtime context
• managed self-updates let systemd restart the daemon after the updater exits into the new binary
• the broken path is covered by regression tests

Validation

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