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>

backend/app/config.py

@@ -0,0 +1,17 @@
+from pydantic_settings import BaseSettings
+
+
+class Settings(BaseSettings):
+    """Application settings loaded from environment variables."""
+
+    DATABASE_URL: str = "postgresql+asyncpg://budget:budget@db:5432/budget_tracker"
+    SECRET_KEY: str = "change-me-in-production"
+    ACCESS_TOKEN_EXPIRE_MINUTES: int = 15
+    REFRESH_TOKEN_EXPIRE_DAYS: int = 7
+    CORS_ORIGINS: list[str] = ["http://localhost:5173"]
+    DEBUG: bool = False
+
+    model_config = {"env_file": ".env", "env_file_encoding": "utf-8"}
+
+
+settings = Settings()

backend/app/database.py

@@ -0,0 +1,31 @@
+from collections.abc import AsyncGenerator
+
+from sqlalchemy.ext.asyncio import (
+    AsyncSession,
+    async_sessionmaker,
+    create_async_engine,
+)
+from sqlalchemy.orm import DeclarativeBase
+
+from app.config import settings
+
+engine = create_async_engine(
+    settings.DATABASE_URL,
+    echo=settings.DEBUG,
+    pool_pre_ping=True,
+)
+
+async_session_factory = async_sessionmaker(
+    engine,
+    class_=AsyncSession,
+    expire_on_commit=False,
+)
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+async def get_session() -> AsyncGenerator[AsyncSession, None]:
+    async with async_session_factory() as session:
+        yield session

backend/app/main.py

@@ -0,0 +1,39 @@
+from contextlib import asynccontextmanager
+from collections.abc import AsyncIterator
+
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+
+from app.config import settings
+from app.database import engine
+
+
+@asynccontextmanager
+async def lifespan(_app: FastAPI) -> AsyncIterator[None]:
+    yield
+    await engine.dispose()
+
+
+def create_app() -> FastAPI:
+    app = FastAPI(
+        title="Budget Tracker API",
+        version="0.1.0",
+        lifespan=lifespan,
+    )
+
+    app.add_middleware(
+        CORSMiddleware,
+        allow_origins=settings.CORS_ORIGINS,
+        allow_credentials=True,
+        allow_methods=["*"],
+        allow_headers=["*"],
+    )
+
+    @app.get("/health")
+    async def health_check() -> dict[str, str]:
+        return {"status": "ok"}
+
+    return app
+
+
+app = create_app()