feat: add Git hooks for code quality checks

[douglaz]

Summary

Add Git hooks to maintain code quality and consistency across all contributors.

Changes

• Add pre-commit hook that checks code formatting
• Add pre-push hook that runs both formatting and clippy checks
• Configure automatic hook setup via nix develop shellHook
• Add Development section to README documenting the hooks

Technical Details

• Hooks detect nix environment and use nix develop -c when available
• Falls back to regular cargo commands if nix is not available
• Hooks are automatically configured when entering nix shell (non-intrusive, only sets if not already configured)
• Uses --workspace flag for clippy to check entire workspace

Testing

• Pre-commit hook tested: blocks commits with unformatted code
• Pre-push hook tested: blocks pushes with formatting or clippy issues
• Automatic setup tested: works correctly in nix develop
• Manual configuration/removal tested: git config commands work as documented

This follows the same pattern successfully implemented in cyberkrill, nostrweet, replicante, and hidraw-rs projects.