Add full-stack BTC portfolio web app

Multi-user FastAPI + React app with JWT auth, SQLite storage, and
CoinGecko price integration. Dockerized with docker-compose.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

btc-portfolio/frontend/package.json

@@ -0,0 +1,21 @@
+{
+  "name": "btc-portfolio-frontend",
+  "version": "1.0.0",
+  "private": true,
+  "dependencies": {
+    "react": "^18.2.0",
+    "react-dom": "^18.2.0",
+    "react-router-dom": "^6.22.0",
+    "react-scripts": "5.0.1",
+    "chart.js": "^4.4.0",
+    "react-chartjs-2": "^5.2.0"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build"
+  },
+  "browserslist": {
+    "production": [">0.2%", "not dead", "not op_mini all"],
+    "development": ["last 1 chrome version", "last 1 firefox version", "last 1 safari version"]
+  }
+}