docs: add CLAUDE.md for Claude Code guidance

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: hasansezertasan

CLAUDE.md

@@ -0,0 +1,51 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+ossin is a Python CLI utility that displays system information (OS, Python environment, platform) using Rich for terminal output. Built with Typer, it supports table, panel, and JSON output formats.
+
+## Development Commands
+
+```bash
+uv sync                          # Install dependencies
+uv run ossin                     # Run the CLI
+uv run ossin --format json       # Run with JSON output
+uv run pytest                    # Run tests
+```
+
+### Linting & Type Checking (CI runs these on Ubuntu only)
+
+```bash
+uv run ruff check src tests      # Lint
+uv run ruff format --check .     # Format check
+uv run mypy                      # Type check (strict mode)
+uv run ty check                  # Type check with ty
+uv run pyrefly check             # Type check with pyrefly
+uv run pyright                   # Type check with pyright
+uv run vulture src tests         # Dead code detection
+uv run validate-pyproject pyproject.toml
+```
+
+## Architecture
+
+- `src/ossin/core.py` — `SystemInfo` TypedDict and `get_system_info()` function (stdlib only: `platform`, `sys`)
+- `src/ossin/cli.py` — Typer app with three output renderers (table, panels, JSON) using Rich
+- `src/ossin/__main__.py` — Entry point, imports and runs `cli.app`
+- Version is dynamic from VCS via hatch-vcs, generated into `src/ossin/_version.py` at build time
+
+## Code Style
+
+- **Ruff** with ALL rules selected, preview mode, unsafe fixes enabled. Ignored rules: B008, COM812, FBT001, FBT003
+- No relative imports allowed (`ban-relative-imports = "all"`)
+- McCabe complexity limit: 4
+- Docstring convention: PEP 257
+- All type checkers run in strict/error-on-warning mode
+- Target Python version: 3.10
+
+## CI/CD
+
+- PR titles must follow **Conventional Commits** format (enforced by check-pr-title workflow)
+- CI runs linters/type-checkers on Ubuntu only; runs the CLI on all three platforms (Ubuntu, macOS, Windows)
+- CD publishes to PyPI via trusted publishing on GitHub release, then triggers Homebrew and Scoop manifest updates