Add pre-commit setup documentation

PRE_COMMIT_SETUP.md

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+# Pre-Commit Hook Setup
+
+This repository uses [pre-commit](https://pre-commit.com/) to enforce code formatting and secret scanning before each commit.
+
+## Prerequisites
+
+- Python 3.x
+- `pip`
+- For C/C++ formatting: `clang-format` (optional — pre-commit will install it via the mirror hook)
+
+## Installation
+
+1. **Install pre-commit:**
+
+   ```bash
+   pip install pre-commit
+   ```
+
+2. **Install the hooks into your local git repo:**
+
+   ```bash
+   pre-commit install
+   ```
+
+   This adds a `.git/hooks/pre-commit` script that runs automatically on every `git commit`.
+
+## Hooks Configured
+
+| Hook | What it does |
+|------|-------------|
+| `autopep8` | Auto-formats Python files to PEP 8 style (max line length 79). Excludes `tools/submission/power/power_checker.py`. |
+| `clang-format` | Auto-formats C and C++ files using the repo's `.clang-format` style file. |
+| `gitleaks` | Scans for hardcoded secrets, API keys, and credentials before they are committed. |
+
+## Usage
+
+Once installed, hooks run automatically on `git commit`. If a hook modifies files (e.g., autopep8 reformats a Python file), the commit is aborted so you can review the changes, then re-stage and commit:
+
+```bash
+git add <reformatted files>
+git commit -m "your message"
+```
+
+## Running Hooks Manually
+
+Run all hooks against all files:
+
+```bash
+pre-commit run --all-files
+```
+
+Run a specific hook:
+
+```bash
+pre-commit run autopep8
+pre-commit run clang-format
+pre-commit run gitleaks
+```
+
+## Skipping Hooks (Not Recommended)
+
+In exceptional cases you can bypass hooks with:
+
+```bash
+git commit --no-verify -m "your message"
+```
+
+Use this sparingly — the hooks exist to keep the codebase consistent and secrets-free.
+
+## Updating Hooks
+
+To update hook versions to the latest revisions specified in `.pre-commit-config.yaml`:
+
+```bash
+pre-commit autoupdate
+```