fix: revert BuildKit cache mounts (BuildKit not default on this host)

Dockerfile

@@ -6,7 +6,7 @@ WORKDIR /app
 # Install dependencies first for better Docker layer caching.
 # This step only reruns if package.json or package-lock.json changes.
 COPY package*.json ./
-RUN --mount=type=cache,target=/root/.npm npm install
+RUN npm install
 
 # Copy the rest of the source code.
 COPY . .
@@ -38,7 +38,7 @@ COPY --from=builder /app/build .
 COPY --from=builder /app/package.json .
 
 # Install only production dependencies for a smaller, cleaner image.
-RUN --mount=type=cache,target=/root/.npm npm install --omit=dev
+RUN npm install --omit=dev
 
 # Copy the resulting .env.production file to .env.
 # adapter-node reads from .env at runtime for non-PUBLIC_ variables.