feat: make API URL configurable and improve code quality

- Add configurable API URL support via environment variables
- Update nginx configuration with environment variable substitution
- Create nginx template for dynamic proxy configuration
- Update Docker configuration for environment variable handling
- Fix hardcoded localhost:8000 references in error messages
- Add proper TypeScript types for health check API
- Format all code with Prettier for consistency
- Update documentation with configuration instructions
- Improve error messages to be environment-agnostic
- Fix duplicate imports and type safety issues

BREAKING: API URL is now configurable via VITE_API_URL (dev) and API_BACKEND_URL (prod)

frontend/Dockerfile

@@ -0,0 +1,34 @@
+# Build stage
+FROM node:20-alpine AS builder
+
+WORKDIR /app
+
+# Copy package files
+COPY package*.json ./
+
+# Install dependencies
+RUN npm i
+
+# Copy source code
+COPY . .
+
+# Build the application
+RUN npm run build
+
+# Production stage
+FROM nginx:alpine
+
+# Copy built application from builder stage
+COPY --from=builder /app/dist /usr/share/nginx/html
+
+# Copy server configuration template
+COPY default.conf.template /etc/nginx/templates/default.conf.template
+
+# Set default API backend URL (can be overridden at runtime)
+ENV API_BACKEND_URL=http://leggend:8000
+
+# Expose port 80
+EXPOSE 80
+
+# Start nginx
+CMD ["nginx", "-g", "daemon off;"]