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>

docker-compose.yml

@@ -1,11 +1,46 @@
 services:
+  db:
+    image: postgres:16-alpine
+    container_name: wealthysmart-db-dev
+    environment:
+      POSTGRES_USER: wealthy_user
+      POSTGRES_PASSWORD: wealthy_pass
+      POSTGRES_DB: wealthysmart
+    ports:
+      - "5433:5432"
+    volumes:
+      - postgres_data:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U wealthy_user -d wealthysmart"]
+      interval: 5s
+      timeout: 3s
+      retries: 5
+
+  backend:
+    build:
+      context: ./backend
+      dockerfile: Dockerfile
+    container_name: wealthysmart-backend-dev
+    environment:
+      DATABASE_URL: postgresql://wealthy_user:wealthy_pass@db:5432/wealthysmart
+    ports:
+      - "8000:8000"
+    volumes:
+      - ./backend:/app
+    depends_on:
+      db:
+        condition: service_healthy
+
   frontend:
     build:
       context: ./frontend
       dockerfile: Dockerfile
     container_name: wealthysmart-frontend-dev
     ports:
-      - "5173:5173"
+      - "5174:5173"
     volumes:
       - ./frontend:/app
       - /app/node_modules
+
+volumes:
+  postgres_data: