feat: Add pyproject.toml with tool configurations

Adds pytest, coverage, black, isort, and mypy configuration to ensure
consistent code formatting and type checking across the project.

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

Author: gmoon

backend/pyproject.toml

@@ -0,0 +1,55 @@
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+asyncio_mode = "auto"
+addopts = "-v --tb=short"
+
+[tool.coverage.run]
+source = ["app"]
+branch = true
+omit = [
+    "*/tests/*",
+    "*/__pycache__/*",
+]
+
+[tool.coverage.report]
+exclude_lines = [
+    "pragma: no cover",
+    "def __repr__",
+    "raise NotImplementedError",
+    "if TYPE_CHECKING:",
+    "if __name__ == .__main__.:",
+]
+fail_under = 70
+show_missing = true
+skip_covered = false
+
+[tool.coverage.html]
+directory = "htmlcov"
+
+[tool.black]
+line-length = 88
+target-version = ['py311']
+include = '\.pyi?$'
+exclude = '''
+/(
+    \.eggs
+  | \.git
+  | \.mypy_cache
+  | \.pytest_cache
+  | \.venv
+  | alembic/versions
+)/
+'''
+
+[tool.isort]
+profile = "black"
+line_length = 88
+skip = ["alembic/versions", ".venv"]
+
+[tool.mypy]
+python_version = "3.11"
+warn_return_any = true
+warn_unused_ignores = true
+disallow_untyped_defs = true
+ignore_missing_imports = true
+exclude = ["alembic/", "tests/"]