feat(opencode): add ibmi column-info tool and harden permissions

- add the get_column_info custom tool for the ibmi-mcp-server and
  relocate its --tools path from a hardcoded absolute path into the
  version-controlled tree via {env:HOME} interpolation
- reorder permission rules so "rm -rf *" (deny) is no longer shadowed
  by "rm *" (ask); last-match-wins now resolves rm -rf to deny
- add allow rules for the Python toolchain (unittest, py_compile,
  venv activation, ruff check/format)
- rename plugin/ to plugins/ to match the documented plural convention
- commit package.json and package-lock.json so the ibmi-gate plugin
  resolves @opencode-ai/plugin on a fresh stow
- correct the README opencode directory description

.config/opencode/package.json

@@ -0,0 +1,5 @@
+{
+  "dependencies": {
+    "@opencode-ai/plugin": "1.18.7"
+  }
+}