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>

frontend/src/index.css

@@ -1 +1,10 @@
 @import 'tailwindcss';
+
+@keyframes fade-in {
+  from { opacity: 0; transform: translateY(8px); }
+  to { opacity: 1; transform: translateY(0); }
+}
+
+.animate-fade-in {
+  animation: fade-in 0.4s ease-out both;
+}