refactor: modernize code quality tooling with Ruff

- Replace black, isort, and flake8 with Ruff (all-in-one linter and formatter)
- Add comprehensive pyproject.toml configuration
- Simplify Makefile code quality targets
- Configure exclusions for venv/.venv in pyproject.toml
- Auto-fix 1,359 linting issues across codebase

Benefits:
- Much faster builds (Ruff is written in Rust)
- Single tool replaces multiple tools
- More comprehensive rule set (UP, B, C4, SIM, PIE, RET, Q)
- All configuration centralized in pyproject.toml
- Better import sorting and formatting consistency

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

pyproject.toml

@@ -0,0 +1,159 @@
+[build-system]
+requires = ["setuptools>=45", "wheel"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "letzshop-product-import"
+version = "0.1.0"
+description = "Multi-tenant e-commerce marketplace platform"
+requires-python = ">=3.11"
+
+# =============================================================================
+# RUFF - Modern All-in-One Linter & Formatter
+# =============================================================================
+[tool.ruff]
+line-length = 88
+target-version = "py311"
+
+# Exclude directories
+exclude = [
+    ".git",
+    ".venv",
+    "venv",
+    "__pycache__",
+    ".mypy_cache",
+    ".pytest_cache",
+    ".ruff_cache",
+    "build",
+    "dist",
+    "alembic/versions",
+]
+
+[tool.ruff.lint]
+# Enable comprehensive rule sets
+select = [
+    "E",     # pycodestyle errors
+    "W",     # pycodestyle warnings
+    "F",     # pyflakes
+    "I",     # isort (import sorting)
+    "N",     # pep8-naming
+    "UP",    # pyupgrade (modern Python syntax)
+    "B",     # flake8-bugbear (common bugs)
+    "C4",    # flake8-comprehensions
+    "SIM",   # flake8-simplify
+    "PIE",   # flake8-pie
+    "RET",   # flake8-return
+    "Q",     # flake8-quotes
+]
+
+# Ignore specific rules
+ignore = [
+    "E501",    # line too long (handled by formatter)
+    "B008",    # do not perform function calls in argument defaults (FastAPI Depends)
+    "RET504",  # unnecessary variable assignment before return
+    "SIM102",  # use a single if statement instead of nested if (sometimes less readable)
+]
+
+# Allow autofix for all rules
+fixable = ["ALL"]
+unfixable = []
+
+# Per-file ignores
+[tool.ruff.lint.per-file-ignores]
+# Ignore import violations in __init__.py files
+"__init__.py" = ["F401", "F403"]
+# Ignore specific rules in test files
+"tests/**/*.py" = ["S101", "PLR2004"]
+# Alembic migrations can have longer lines and specific patterns
+"alembic/versions/*.py" = ["E501", "F401"]
+
+# Import sorting configuration (replaces isort)
+[tool.ruff.lint.isort]
+known-first-party = ["app", "models", "middleware", "tasks", "storage", "scripts"]
+section-order = ["future", "standard-library", "third-party", "first-party", "local-folder"]
+split-on-trailing-comma = true
+
+# Formatter configuration (replaces black)
+[tool.ruff.format]
+quote-style = "double"
+indent-style = "space"
+skip-magic-trailing-comma = false
+line-ending = "auto"
+
+# =============================================================================
+# MYPY - Static Type Checker
+# =============================================================================
+[tool.mypy]
+python_version = "3.11"
+warn_return_any = true
+warn_unused_configs = true
+disallow_untyped_defs = false
+ignore_missing_imports = true
+exclude = [
+    "^\\.venv/",
+    "^venv/",
+    "^build/",
+    "^dist/",
+    "^alembic/versions/",
+]
+
+# Per-module options
+[[tool.mypy.overrides]]
+module = "tests.*"
+ignore_errors = true
+
+[[tool.mypy.overrides]]
+module = "alembic.*"
+ignore_errors = true
+
+# =============================================================================
+# PYTEST - Testing
+# =============================================================================
+[tool.pytest.ini_options]
+minversion = "7.0"
+testpaths = ["tests"]
+python_files = ["test_*.py", "*_test.py"]
+python_classes = ["Test*"]
+python_functions = ["test_*"]
+addopts = [
+    "-v",
+    "--strict-markers",
+    "--strict-config",
+    "--color=yes",
+]
+markers = [
+    "unit: Unit tests",
+    "integration: Integration tests",
+    "slow: Slow running tests",
+]
+filterwarnings = [
+    "ignore::DeprecationWarning",
+]
+
+# =============================================================================
+# COVERAGE
+# =============================================================================
+[tool.coverage.run]
+source = ["app", "models", "middleware", "tasks", "storage"]
+omit = [
+    "*/tests/*",
+    "*/__pycache__/*",
+    "*/venv/*",
+    "*/.venv/*",
+    "*/alembic/*",
+    "*/scripts/*",
+]
+
+[tool.coverage.report]
+precision = 2
+show_missing = true
+skip_covered = false
+exclude_lines = [
+    "pragma: no cover",
+    "def __repr__",
+    "raise AssertionError",
+    "raise NotImplementedError",
+    "if __name__ == .__main__.:",
+    "if TYPE_CHECKING:",
+    "if typing.TYPE_CHECKING:",
+]