The opencode-serve unit ran with systemd's minimal default PATH, so
shell commands invoked by the agent (git, make, nix, node, rg, etc.)
were not found. Set systemd.services.opencode-serve.path on both sgx
and amd to a common dev toolset.
Mirror of the sgx opencode setup: systemd service on port 4196 fronted
by nginx with a per-host ACME cert (DNS-01 via internetbs). Adds amd
key + path rule to .sops.yaml so secrets under .secrets/amd/ encrypt
for the host.
