feat(frontend): enhance API credentials system and build configuration

Add real API support in demo mode with credential checking, implement build-time version injection from package.json, and refactor update checking with 24-hour caching. Migrate landing page from Vue to Astro with comprehensive UI components including Hero, Features, Benefits, and Tech Stack sections. Update CI/CD workflow with expanded cache paths and security scanner version pinned.

landing/Dockerfile

@@ -0,0 +1,32 @@
+# Stage 1: Build stage
+FROM node:18-alpine AS builder
+
+# Set working directory
+WORKDIR /app
+
+# Copy package files
+COPY package*.json ./
+
+# Install dependencies
+RUN npm ci --only=production
+
+# Copy source code
+COPY . .
+
+# Build the application
+RUN npm run build
+
+# Stage 2: Production stage
+FROM nginx:alpine
+
+# Copy built files from builder stage
+COPY --from=builder /app/dist /usr/share/nginx/html
+
+# Copy nginx configuration
+COPY nginx.conf /etc/nginx/nginx.conf
+
+# Expose port 80
+EXPOSE 80
+
+# Start nginx
+CMD ["nginx", "-g", "daemon off;"]