docs: add git integration demo example

Author: d-oit

examples/git_integration_demo.md

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+# Code-Guardian Git Integration Demo
+
+This document demonstrates the new git integration features in Code-Guardian.
+
+## Features
+
+### 1. Pre-commit Hook Installation
+
+Install the pre-commit hook to automatically run Code-Guardian before each commit:
+
+```bash
+# Install the hook
+code-guardian git install-hook
+
+# The hook will now run automatically on every commit
+git commit -m "Your commit message"
+```
+
+### 2. Staged Files Scanning
+
+Scan only staged files instead of the entire repository:
+
+```bash
+# Scan only staged files
+code-guardian pre-commit --staged-only
+
+# Fast scan of staged files (critical issues only)
+code-guardian pre-commit --staged-only --fast
+```
+
+### 3. Git Integration Commands
+
+```bash
+# List currently staged files
+code-guardian git staged
+
+# Install pre-commit hook
+code-guardian git install-hook
+
+# Uninstall pre-commit hook  
+code-guardian git uninstall-hook
+```
+
+## Workflow Integration
+
+### Typical Developer Workflow
+
+1. **One-time setup**: Install the pre-commit hook
+   ```bash
+   code-guardian git install-hook
+   ```
+
+2. **Daily development**: Work normally - the hook runs automatically
+   ```bash
+   # Make changes
+   vim src/main.rs
+   
+   # Stage changes
+   git add src/main.rs
+   
+   # Commit (hook runs automatically)
+   git commit -m "Add new feature"
+   ```
+
+3. **Manual scanning**: Check staged files before committing
+   ```bash
+   # See what files are staged
+   code-guardian git staged
+   
+   # Run manual pre-commit check
+   code-guardian pre-commit --staged-only --fast
+   ```
+
+### CI/CD Integration
+
+The git integration works seamlessly with CI/CD pipelines:
+
+```yaml
+# .github/workflows/code-quality.yml
+- name: Run Code-Guardian on changed files
+  run: |
+    # Get list of changed files in PR
+    git fetch origin main
+    git diff --name-only origin/main... > changed_files.txt
+    
+    # Run Code-Guardian on changed files
+    code-guardian scan --files-from changed_files.txt
+```
+
+## Benefits
+
+- **Faster feedback**: Catch issues at commit time, not in CI
+- **Focused scanning**: Only scan files you're actually changing
+- **Team adoption**: Automatic enforcement through git hooks
+- **Flexible**: Works with both individual commits and CI/CD pipelines
+
+## Technical Implementation
+
+The git integration uses:
+- `git diff --cached --name-only` to get staged files
+- `git rev-parse --show-toplevel` to find repository root
+- Native git commands for maximum compatibility
+- Graceful fallback to directory scanning when not in a git repo
+
+## Configuration
+
+The pre-commit hook uses these default settings:
+- `--staged-only`: Only scan staged files
+- `--fast`: Quick scan mode (critical issues only)
+
+You can customize by editing the hook file directly or using a configuration file.