feat: add test suite, tox, pre-commit, and ruff formatting

- tests/: 107 unit tests across config, cache, docker_auth, storage,
  and FastAPI routes; all passing under pytest-asyncio auto mode
- tox.ini: runs pytest via uvx --with tox-uv tox (py311)
- .pre-commit-config.yaml: ruff lint + ruff-format at v0.15.12
- pyproject.toml: pytest config (asyncio_mode=auto), ruff config
  (line-length=140), tox/pre-commit added to dev extras
- Makefile: test/tox/pre-commit targets via uvx --python 3.11
- Source files reformatted by ruff-format (no logic changes)

Makefile

@@ -1,4 +1,4 @@
-.PHONY: build install dev clean test lint format docker-build docker-up docker-down docker-logs docker-rebuild docker-clean docker-restart
+.PHONY: build install dev clean test lint format pre-commit tox docker-build docker-up docker-down docker-logs docker-rebuild docker-clean docker-restart
 
 build:
 	docker build --no-cache -t artifactapi:latest .
@@ -17,7 +17,13 @@ clean:
 	rm -rf *.egg-info/
 
 test:
-	uv run pytest
+	uvx --python 3.11 --with tox-uv tox
+
+tox:
+	uvx --python 3.11 --with tox-uv tox
+
+pre-commit:
+	uvx --python 3.11 pre-commit run --all-files
 
 lint:
 	uv run ruff check --fix .