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

README.md

@@ -11,7 +11,7 @@ The zsh theme and plugins are installed manually rather than through a plugin ma
 ├── .zshrc                  # zsh config: PATH, history, completions, prompt, aliases
 ├── .config/
 │   ├── nvim/               # Neovim config (init.lua, lua/, after/, queries/)
-│   └── opencode/           # opencode config (agents, skills, plugins, rules)
+│   └── opencode/           # opencode config (commands, plugins, MCP tools, rules)
 └── .scripts/               # Standalone shell scripts (on $PATH)
     └── hello.sh
 ```