feat: add RobloxClient and package exports

- Add client.py with RobloxClient class (migrated from clothing-upload-bot)
- Credentials passed via constructor instead of module-level env globals
- Supports async context manager and manual close()
- Add __init__.py exporting RobloxClient, RateLimitError, and models
- Add .gitignore

pyproject.toml

@@ -6,6 +6,7 @@ requires-python = ">=3.13"
 dependencies = [
     "httpx>=0.25.0",
 ]
+license = "MIT"
 
 [build-system]
 requires = ["hatchling"]