Fix: update Dockerfile with build verification and npm install

Dockerfile

@@ -1,37 +1,41 @@
 # ---------------------------------------------------------
-# ---------------------------------------------------------
 #  Build stage
 # ---------------------------------------------------------
 FROM node:18-alpine AS builder
 
-# Install git (only needed for npm postinstall scripts)
+# Install git (needed by some npm packages)
 RUN apk add --no-cache git
 
 WORKDIR /app
 
-# Copy package files
-COPY package.json ./
+# Copy only package files first (leverages caching)
+COPY package.json package-lock.json* ./
+
+# Install dependencies (npm ci uses lockfile, but we don't have it)
+# Using npm install instead for broader compatibility
 RUN npm install
 
-# Copy the rest of the source tree
+# Copy source files
 COPY . .
 
-# Build the production bundle (Vite outputs to `dist/`)
+# Build the production bundle (outputs to /app/dist)
 ENV NODE_ENV=production
 RUN npm run build
 
-# DEBUG: Confirm build output exists before proceeding
-RUN echo "=== BUILD OUTPUT CHECK ===" && \
+# DEBUG: Verify the build output exists before proceeding
+RUN echo "=== BUILD OUTPUT ===" && \
     ls -la /app/dist && \
-    cat /app/dist/index.html 2>/dev/null | head -n 5 || echo "ERROR: INDEX NOT FOUND - build may have failed silently"
+    cat /app/dist/index.html | head -n 10 || echo "ERROR: index.html missing"
 
 # ---------------------------------------------------------
-#  Production stage – tiny static server (nginx)
+#  Production stage – nginx serving the static files
 # ---------------------------------------------------------
 FROM nginx:alpine
 
+# Custom nginx config
 COPY nginx.conf /etc/nginx/conf.d/default.conf
 
+# Copy the compiled React app into nginx's web root
 COPY --from=builder /app/dist /usr/share/nginx/html
 
 EXPOSE 80