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.prod.yml

@@ -1,4 +1,47 @@
 services:
+  db:
+    image: postgres:16-alpine
+    container_name: wealthysmart-db-prod
+    restart: unless-stopped
+    environment:
+      POSTGRES_USER: ${POSTGRES_USER}
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD}
+      POSTGRES_DB: ${POSTGRES_DB}
+    volumes:
+      - postgres_data:/var/lib/postgresql/data
+    networks:
+      - wealthysmart-network
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER} -d ${POSTGRES_DB}"]
+      interval: 10s
+      timeout: 5s
+      retries: 5
+
+  backend:
+    build:
+      context: ./backend
+      dockerfile: Dockerfile.prod
+    container_name: wealthysmart-backend-prod
+    restart: unless-stopped
+    environment:
+      DATABASE_URL: postgresql://${POSTGRES_USER}:${POSTGRES_PASSWORD}@db:5432/${POSTGRES_DB}
+      SECRET_KEY: ${SECRET_KEY}
+      ADMIN_USERNAME: ${ADMIN_USERNAME}
+      ADMIN_PASSWORD: ${ADMIN_PASSWORD}
+    expose:
+      - "8000"
+    networks:
+      - wealthysmart-network
+    depends_on:
+      db:
+        condition: service_healthy
+    healthcheck:
+      test: ["CMD", "python", "-c", "import urllib.request; urllib.request.urlopen('http://localhost:8000/')"]
+      interval: 15s
+      timeout: 5s
+      retries: 3
+      start_period: 10s
+
   frontend:
     build:
       context: ./frontend
@@ -12,7 +55,10 @@ services:
     expose:
       - "80"
     networks:
+      - wealthysmart-network
       - nginx-prod-network
+    depends_on:
+      - backend
     healthcheck:
       test: ["CMD", "wget", "--quiet", "--tries=1", "--spider", "http://127.0.0.1/"]
       interval: 30s
@@ -20,5 +66,12 @@ services:
       retries: 3
 
 networks:
+  wealthysmart-network:
+    driver: bridge
+    name: wealthysmart-network-prod
   nginx-prod-network:
     external: true
+
+volumes:
+  postgres_data:
+    name: wealthysmart-postgres-prod-data