Add opencode.json to every agent directory

Every agent must have opencode.json with permission: allow,
regardless of adapter type. Without it, opencode auto-rejects
file access outside the agent's cwd.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

engineering/regina/opencode.json

@@ -0,0 +1,7 @@
+{
+  "$schema": "https://opencode.ai/config.json",
+  "permission": "allow",
+  "experimental": {
+    "snapshots": false
+  }
+}