test(backend): Add pytest testing infrastructure

- Add pytest, pytest-asyncio, pytest-mock to dev dependencies
- Configure pytest in pyproject.toml with async support
- Create tests directory structure with conftest.py
- Set up unit test framework for connector testing
- Enable automated testing for backend components

surfsense_backend/pyproject.toml

@@ -67,6 +67,10 @@ dependencies = [
 [dependency-groups]
 dev = [
     "ruff>=0.12.5",
+    "pytest>=8.0.0",
+    "pytest-asyncio>=0.24.0",
+    "pytest-mock>=3.14.0",
+    "httpx>=0.28.0",
 ]
 
 [tool.ruff]
@@ -158,6 +162,14 @@ known-first-party = ["app"]
 force-single-line = false
 combine-as-imports = true
 
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+python_files = ["test_*.py"]
+python_classes = ["Test*"]
+python_functions = ["test_*"]
+asyncio_mode = "auto"
+asyncio_default_fixture_loop_scope = "function"
+
 [tool.setuptools.packages.find]
 where = ["."]
 include = ["app*", "alembic*"]