Codex skill for development added. Tested by using it to set up Play Palace.

.codex/skills/linux-game-manager-dev/references/tooling-prereqs.md

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+# Tooling Prerequisites
+
+## Required Tool for Bash Changes
+
+- `shellcheck` is mandatory whenever editing any bash/sh file in this repository.
+- If `shellcheck` is not available, prompt the user to install it before continuing validation.
+
+Check availability:
+
+```bash
+command -v shellcheck
+```
+
+## Prompt Template
+
+Use this exact style when missing:
+
+`shellcheck is required for bash/sh edits in linux-game-manager. Please install it, then I will continue validation.`
+
+## Install Commands by Common Distro Family
+
+- Arch/Manjaro:
+  - `sudo pacman -S shellcheck`
+- Debian/Ubuntu/Linux Mint/Pop!_OS:
+  - `sudo apt update && sudo apt install -y shellcheck`
+- Fedora/RHEL/CentOS Stream:
+  - `sudo dnf install -y ShellCheck`
+- openSUSE:
+  - `sudo zypper install -y ShellCheck`
+- Alpine:
+  - `sudo apk add shellcheck`
+
+If distro is unknown, ask the user what distribution they are on and provide the matching package command.
+
+## Notes for LGM Collaboration
+
+- Do not skip shellcheck for “small” bash changes.
+- Fix all shellcheck errors; warnings may be suppressed only when required by sourced-global patterns and with a short comment.