feat: implement client architecture and sandbox environment

Introduces the core Wrenn client and a dedicated sandbox execution
environment. This includes automated model generation and a custom
exception hierarchy to support robust integration.

- Add `WrennClient` in `src/wrenn/client.py` for API interaction.
- Implement `Sandbox` in `src/wrenn/sandbox.py` for isolated execution.
- Add Pydantic/model support via `_generated.py`.
- Define project-specific error types in `exceptions.py`.
- Include AGENTS.md documentation for specialized logic.
- Add comprehensive unit and integration tests.
- Update build system (Makefile, uv.lock, pyproject.toml) and LICENSE.

pyproject.toml

@@ -8,7 +8,9 @@ authors = [
 ]
 requires-python = ">=3.13"
 dependencies = [
+    "email-validator>=2.3.0",
     "httpx>=0.28.1",
+    "httpx-ws>=0.9.0",
     "pydantic>=2.12.5",
 ]
 
@@ -22,5 +24,11 @@ dev = [
     "mypy>=1.20.0",
     "pytest>=9.0.3",
     "pytest-asyncio>=1.3.0",
+    "respx>=0.23.1",
     "ruff>=0.15.10",
 ]
+
+[tool.pytest.ini_options]
+markers = [
+    "integration: integration tests (require live server)",
+]