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/Dockerfile

@@ -0,0 +1,16 @@
+FROM node:18-alpine AS build
+
+WORKDIR /app
+COPY package.json ./
+RUN npm install
+COPY . .
+ARG REACT_APP_API_URL=http://localhost:8000
+ENV REACT_APP_API_URL=$REACT_APP_API_URL
+RUN npm run build
+
+FROM node:18-alpine
+RUN npm install -g serve
+WORKDIR /app
+COPY --from=build /app/build ./build
+EXPOSE 3000
+CMD ["serve", "-s", "build", "-l", "3000"]