Bust Docker cache to fetch updated tinypdf-plus with dist

backend/Dockerfile

@@ -10,8 +10,8 @@ COPY package*.json ./
 # Copy prisma directory if it exists, otherwise we'll handle it
 COPY prisma ./prisma/
 
-# Install dependencies
-RUN npm install
+# Install dependencies (CACHE BUST: 2025-01-08)
+RUN npm install && echo "Cache bust: tinypdf-plus updated with dist"
 
 # Copy source
 COPY . .