Add budget module: FastAPI backend + React frontend

Backend: FastAPI + PostgreSQL with models for accounts, transactions,
and categories. Auto-categorization from merchant patterns, token auth,
CRUD endpoints, and seed data for 16 categories and 4 bank accounts.

Frontend: Login, Dashboard (account balances + recent charges),
Transactions (full CRUD table with search/filter), Cash & Transfers
view. Dark theme with emerald/cyan accents, responsive layout.

Infrastructure: Updated docker-compose for backend + db services,
nginx proxy config for API routing, deploy workflow with secrets.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/config.py

@@ -0,0 +1,15 @@
+from pydantic_settings import BaseSettings
+
+
+class Settings(BaseSettings):
+    DATABASE_URL: str = "postgresql://wealthy_user:wealthy_pass@db:5432/wealthysmart"
+    SECRET_KEY: str = "change-me-in-production"
+    ACCESS_TOKEN_EXPIRE_MINUTES: int = 60 * 24 * 30  # 30 days
+    ADMIN_USERNAME: str = "admin"
+    ADMIN_PASSWORD: str = "admin"
+
+    class Config:
+        env_file = ".env"
+
+
+settings = Settings()