fix: reduce Kaniko disk usage in Node.js Dockerfiles

- Combine production stage RUN commands into single layers
  (each RUN triggers a full Kaniko filesystem snapshot)
- Remove BuildKit --mount=type=cache for pnpm store
  (Kaniko builds are ephemeral in CI, cache is never reused)
- Remove syntax=docker/dockerfile:1 directive (no longer needed
  without BuildKit cache mounts)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/Dockerfile

@@ -1,6 +1,3 @@
-# syntax=docker/dockerfile:1
-# Enable BuildKit features for cache mounts
-
 # Base image for all stages
 # Uses Debian slim (glibc) for consistency with API/orchestrator and to prevent
 # future native addon compatibility issues with Alpine's musl libc.
@@ -27,9 +24,8 @@ COPY packages/ui/package.json ./packages/ui/
 COPY packages/config/package.json ./packages/config/
 COPY apps/web/package.json ./apps/web/
 
-# Install dependencies with pnpm store cache
-RUN --mount=type=cache,id=pnpm-store,target=/root/.local/share/pnpm/store \
-    pnpm install --frozen-lockfile
+# Install dependencies (no cache mount — Kaniko builds are ephemeral in CI)
+RUN pnpm install --frozen-lockfile
 
 # ======================
 # Builder stage
@@ -79,19 +75,15 @@ RUN mkdir -p ./apps/web/public
 # ======================
 FROM node:24-slim AS production
 
-# Remove npm (unused in production — we use pnpm) to reduce attack surface
-RUN rm -rf /usr/local/lib/node_modules/npm /usr/local/bin/npm /usr/local/bin/npx
-
-# Install pnpm (needed for pnpm start command)
-RUN corepack enable && corepack prepare pnpm@10.27.0 --activate
-
 # Install dumb-init for proper signal handling (static binary from GitHub,
 # avoids apt-get which fails under Kaniko with bookworm GPG signature errors)
 ADD https://github.com/Yelp/dumb-init/releases/download/v1.2.5/dumb-init_1.2.5_x86_64 /usr/local/bin/dumb-init
-RUN chmod 755 /usr/local/bin/dumb-init
 
-# Create non-root user
-RUN groupadd -g 1001 nodejs && useradd -m -u 1001 -g nodejs nextjs
+# Single RUN to minimize Kaniko filesystem snapshots (each RUN = full snapshot)
+RUN rm -rf /usr/local/lib/node_modules/npm /usr/local/bin/npm /usr/local/bin/npx \
+    && corepack enable && corepack prepare pnpm@10.27.0 --activate \
+    && chmod 755 /usr/local/bin/dumb-init \
+    && groupadd -g 1001 nodejs && useradd -m -u 1001 -g nodejs nextjs
 
 WORKDIR /app