orchestrator: run on the opencode backend + auto-start on boot

Switch the cc-ci-orchestrator agent (cc-ci-plan/agents.toml) from the claude
backend to the opencode backend so it attaches to the shared opencode web
server (opencode-web.service, 127.0.0.1:4096) and is reachable for Remote
Control at https://oc.commoninternet.net under the /srv/cc-ci-orch project.
Model = opencode/glm-5.2 (same provider family as the weekly upgrader /
supervisor). resume=false — the opencode backend has no --resume equivalent
(a fresh session per launch, matching the existing launch-opencode.sh shape).

Add a cc-ci-orchestrator.service systemd unit so on boot it runs
'agents.py up orchestrator' after opencode-web.service is up — the same
reboot-resilience shape lichen-orchestrator / project-orchestrator already
have. KillMode=process so a rebuild that merely touches this unit does not
tear down the shared tmux server and every agent session with it.

No secrets: the diff is only config + comments (paths, model names, unit
definition).

cc-ci-plan/agents.toml

@@ -53,8 +53,9 @@ log_dir = "/srv/cc-ci/.cc-ci-logs"
 [[agent]]
 name    = "orchestrator"       # tmux session: cc-ci-orchestrator
 kind    = "persistent"
-model   = "claude-opus-4-8"
-resume  = true                 # claude --resume <state/orchestrator.id>
+backend = "opencode"           # attached to the shared opencode web server (oc.commoninternet.net)
+model   = "opencode/glm-5.2"   # opencode backend; visible at https://oc.commoninternet.net
+resume  = false                # opencode backend has no --resume equivalent (fresh session each launch)
 watch   = "heal"               # restart if dead / FATAL / backend-mismatch; never stall-reboot
 wake    = { interval = 3600, prompt_file = "ai-progress-monitor-prompt.txt" }
 prompt  = """