opencode: run task-tool subagents on deepseek-v4-pro

Main/driving sessions stay glm-5.2 (set per-launch via --model); the built-in
'general' agent used by the task tool runs opencode/deepseek-v4-pro: ~3-5x cheaper
per token with near-free cache hits, and the weekly /upgrade-all spends most of its
budget in per-recipe subagents.

Placement matters and was got wrong once (2026-08-04 config sat in the orchestrator
repo and never bound; the whole 2026-08-07 run billed as glm): sessions launched by
launch-upgrader.py pass no --dir, so they inherit the opencode serve process's
project (WorkingDirectory=/srv/cc-ci-orch/cc-ci = THIS repo), and task-tool
subagents inherit their parent session's directory. This file is therefore the
project config those subagents actually resolve.

Verified end-to-end 2026-08-10 with the launcher's exact invocation: parent session
modelID=glm-5.2, spawned subagent modelID=deepseek-v4-pro (read back from the
opencode session DB, not from config inspection).

opencode.json

@@ -0,0 +1,8 @@
+{
+  "$schema": "https://opencode.ai/config.json",
+  "agent": {
+    "general": {
+      "model": "opencode/deepseek-v4-pro"
+    }
+  }
+}