fix: restore 3072 MB heap for frontend — single-thread needs ~1.9 GB

cpus:1 eliminates parallel webpack workers (the root OOM cause).
But 2048 MB was too tight for a single V8 heap; the GC died at ~1855 MB.
With only one worker process, 3072 MB is safe — the builder sees one 3 GB
Node process instead of N×3 GB parallel workers that triggered the original
OOMKilled.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Dockerfile

@@ -73,7 +73,7 @@ RUN pnpm install --frozen-lockfile=false
 RUN NODE_OPTIONS="--max-old-space-size=3072" pnpm run build:backend
 RUN NODE_OPTIONS="--max-old-space-size=3072" pnpm run build:workers
 RUN NODE_OPTIONS="--max-old-space-size=3072" pnpm run build:cron
-RUN NODE_OPTIONS="--max-old-space-size=2048" pnpm run build:frontend
+RUN NODE_OPTIONS="--max-old-space-size=3072" pnpm run build:frontend
 
 # Drop dev junk to shrink the runtime image.
 RUN find . -name ".git" -type d -prune -exec rm -rf {} + 2>/dev/null || true \