Add pyproject.toml for consolidated project configuration and replace Black, isort, and Flake8 with Ruff

- Introduced `pyproject.toml` to centralize backend tool configurations (e.g., Ruff, mypy, coverage, pytest).
- Replaced Black, isort, and Flake8 with Ruff for linting, formatting, and import sorting.
- Updated `requirements.txt` to include Ruff and remove replaced tools.
- Added `Makefile` to streamline development workflows with commands for linting, formatting, type-checking, testing, and cleanup.

backend/Makefile

@@ -0,0 +1,82 @@
+.PHONY: help lint lint-fix format format-check type-check test test-cov validate clean install-dev
+
+# Default target
+help:
+	@echo "🚀 FastAPI Backend - Development Commands"
+	@echo ""
+	@echo "Quality Checks:"
+	@echo "  make lint          - Run Ruff linter (check only)"
+	@echo "  make lint-fix      - Run Ruff linter with auto-fix"
+	@echo "  make format        - Format code with Ruff"
+	@echo "  make format-check  - Check if code is formatted"
+	@echo "  make type-check    - Run mypy type checking"
+	@echo "  make validate      - Run all checks (lint + format + types)"
+	@echo ""
+	@echo "Testing:"
+	@echo "  make test          - Run pytest"
+	@echo "  make test-cov      - Run pytest with coverage report"
+	@echo ""
+	@echo "Setup:"
+	@echo "  make install-dev   - Install all development dependencies"
+	@echo "  make clean         - Remove cache and build artifacts"
+
+# ============================================================================
+# Code Quality
+# ============================================================================
+
+lint:
+	@echo "🔍 Running Ruff linter..."
+	@ruff check app/ tests/
+
+lint-fix:
+	@echo "🔧 Running Ruff linter with auto-fix..."
+	@ruff check --fix app/ tests/
+
+format:
+	@echo "✨ Formatting code with Ruff..."
+	@ruff format app/ tests/
+
+format-check:
+	@echo "📋 Checking code formatting..."
+	@ruff format --check app/ tests/
+
+type-check:
+	@echo "🔎 Running mypy type checking..."
+	@mypy app/
+
+validate: lint format-check type-check
+	@echo "✅ All quality checks passed!"
+
+# ============================================================================
+# Testing
+# ============================================================================
+
+test:
+	@echo "🧪 Running tests..."
+	@IS_TEST=True pytest
+
+test-cov:
+	@echo "🧪 Running tests with coverage..."
+	@IS_TEST=True pytest --cov=app --cov-report=term-missing --cov-report=html -n 0
+	@echo "📊 Coverage report generated in htmlcov/index.html"
+
+# ============================================================================
+# Setup & Cleanup
+# ============================================================================
+
+install-dev:
+	@echo "📦 Installing development dependencies..."
+	@pip install -r requirements.txt
+	@echo "✅ Development environment ready!"
+
+clean:
+	@echo "🧹 Cleaning up..."
+	@find . -type d -name "__pycache__" -exec rm -rf {} + 2>/dev/null || true
+	@find . -type d -name ".pytest_cache" -exec rm -rf {} + 2>/dev/null || true
+	@find . -type d -name ".mypy_cache" -exec rm -rf {} + 2>/dev/null || true
+	@find . -type d -name ".ruff_cache" -exec rm -rf {} + 2>/dev/null || true
+	@find . -type d -name "*.egg-info" -exec rm -rf {} + 2>/dev/null || true
+	@find . -type d -name "htmlcov" -exec rm -rf {} + 2>/dev/null || true
+	@find . -type f -name ".coverage" -delete 2>/dev/null || true
+	@find . -type f -name "*.pyc" -delete 2>/dev/null || true
+	@echo "✅ Cleanup complete!"