feat: complete project scaffolding with high-quality Rust setup

[AngeloGiacco]

This commit establishes the complete project structure for agent-precommit,
a smart pre-commit hook system that detects human vs AI agent commits.

Core features implemented:

• Rust project with extremely strict linting (Clippy + rustfmt)
• Mode detection for human, agent, and CI environments
• Command execution with timeout and parallel support
• Configuration management with presets (Python, Node, Rust, Go)
• Full CLI with init, install, run, detect, list, and validate commands

Quality & Linting:

• Strict Clippy configuration denying unsafe code, unwrap, panic, todo
• Comprehensive rustfmt configuration for consistent formatting
• Pre-commit hooks for the project itself
• GitHub Actions CI with format, lint, test, MSRV, and security checks

Distribution:

• Cargo publishing support
• Python pip distribution via maturin
• Cross-platform release workflow (Linux, macOS, Windows)
• Homebrew formula generation
• Shell installer script generation

Project structure:

• src/core/: detector, executor, runner, git operations, error handling
• src/cli/: clap-based CLI with subcommands
• src/config/: TOML configuration with validation
• src/checks/: built-in checks and pre-commit integration
• src/presets/: language-specific configuration presets