docs(SYSTEM_PROMPT.md): add guidelines for using shell commands in Windows/PowerShell to avoid command length issues

SYSTEM_PROMPT.md

@@ -46,3 +46,23 @@
 
 - **Edit only in source**: Skills, agent bodies, and this system prompt live in `C:\sources\oh-my-skills` (`skills/`, `agents/`, `SYSTEM_PROMPT.md`). Modify them ONLY there.
 - **Never edit synced copies**: `~/.agents/skills`, `~/.agents/agents`, and global prompt files (e.g. `~/.claude/CLAUDE.md`) are sync targets; the user syncs them manually.
+
+---
+
+## Shell commands on Windows/PowerShell
+
+Never pass long or multiline commands directly to the shell (pwsh/PowerShell).
+Windows has a ~8191-character command-line length limit, and long inline
+commands (heredocs, multiline strings, long argument lists) frequently fail
+with "malformed syntax" or "command line too long" errors.
+
+Instead:
+- Write the command/code to a script file first (`.ps1`, `.py`, `.sh`, etc.)
+  using the file-writing tools, then execute the file with a short command
+  (e.g. `.\script.ps1` or `python script.py`).
+- If the command needs large input (long lists of files, big data), write
+  that input to a file (JSON/CSV/txt) and have the script read from it,
+  rather than passing it as inline arguments.
+- Only run short, simple commands directly in the shell.
+
+---