chore: initial project setup

Phase 0 — full project scaffold with:
- Backend: FastAPI + SQLAlchemy 2.0 async + Alembic + PostgreSQL 16
- Frontend: React 18 + TypeScript + Vite + Tailwind CSS + shadcn/ui
- Docker Compose (prod + dev override with hot-reload)
- Health endpoint, CORS config, API proxy, env template

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -0,0 +1,46 @@
+services:
+  db:
+    image: postgres:16-alpine
+    restart: unless-stopped
+    environment:
+      POSTGRES_USER: ${POSTGRES_USER:-budget}
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:-budget}
+      POSTGRES_DB: ${POSTGRES_DB:-budget_tracker}
+    ports:
+      - "${DB_PORT:-5432}:5432"
+    volumes:
+      - pgdata:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER:-budget}"]
+      interval: 5s
+      timeout: 5s
+      retries: 5
+
+  backend:
+    build:
+      context: ./backend
+      dockerfile: Dockerfile
+    restart: unless-stopped
+    environment:
+      DATABASE_URL: postgresql+asyncpg://${POSTGRES_USER:-budget}:${POSTGRES_PASSWORD:-budget}@db:5432/${POSTGRES_DB:-budget_tracker}
+      SECRET_KEY: ${SECRET_KEY:-change-me-in-production}
+      CORS_ORIGINS: '["http://localhost:5173","http://localhost:3000"]'
+      DEBUG: ${DEBUG:-false}
+    ports:
+      - "${BACKEND_PORT:-8000}:8000"
+    depends_on:
+      db:
+        condition: service_healthy
+
+  frontend:
+    build:
+      context: ./frontend
+      dockerfile: Dockerfile
+    restart: unless-stopped
+    ports:
+      - "${FRONTEND_PORT:-3000}:80"
+    depends_on:
+      - backend
+
+volumes:
+  pgdata: