fix: make source maps opt-in to restore v1.67.0 memory baseline

Production source maps (--enable-source-maps) caused a ~50% memory increase
(600MB to 1000MB) in v1.68.0. Node.js loads all .map files into memory when
this flag is enabled, and Next.js server chunks generate hundreds of map files.

Changes:
- Guard productionBrowserSourceMaps and serverSourceMaps behind
  HOMARR_ENABLE_SOURCE_MAPS env var (default off)
- Guard .map copy step and NODE_OPTIONS in Dockerfile behind
  ENABLE_SOURCE_MAPS build arg (default false)
- run.sh checks HOMARR_ENABLE_SOURCE_MAPS before setting --enable-source-maps
- Add Docker-based memory regression CI job (<700MB threshold)

Closes #6123

Dockerfile

@@ -20,16 +20,18 @@ ARG DISABLE_REDIS_LOGS='true'
 
 RUN corepack enable pnpm && pnpm build
 
-# The standalone output tracing omits server chunk source maps (.next/server/**/*.map), which is
-# where production Node stack frames point. Copy the .map files into the standalone tree (preserving
-# directory structure) so the existing standalone COPY ships them, keeping traces readable.
-# See https://github.com/homarr-labs/homarr/issues/5891
-RUN cd apps/nextjs/.next/server && \
-    find . -name '*.map' | while IFS= read -r map; do \
-      dest="../standalone/apps/nextjs/.next/server/$map"; \
-      mkdir -p "$(dirname "$dest")"; \
-      cp "$map" "$dest"; \
-    done
+# Copy server chunk source maps into standalone output when enabled.
+# Off by default to avoid the significant memory overhead of --enable-source-maps in Node.js.
+# See https://github.com/homarr-labs/homarr/issues/6123 and https://github.com/nodejs/node/issues/46140
+ARG ENABLE_SOURCE_MAPS=false
+RUN if [ "$ENABLE_SOURCE_MAPS" = "true" ]; then \
+      cd apps/nextjs/.next/server && \
+      find . -name '*.map' | while IFS= read -r map; do \
+        dest="../standalone/apps/nextjs/.next/server/$map"; \
+        mkdir -p "$(dirname "$dest")"; \
+        cp "$map" "$dest"; \
+      done; \
+    fi
 
 FROM base AS runner
 WORKDIR /app
@@ -75,9 +77,9 @@ ENV DB_DRIVER='better-sqlite3'
 ENV AUTH_PROVIDERS='credentials'
 ENV REDIS_IS_EXTERNAL='false'
 ENV NODE_ENV='production'
-# Tell Node to symbolicate stack traces using the shipped .map files so production logs
-# show original source locations instead of minified frames, see https://github.com/homarr-labs/homarr/issues/5891
-ENV NODE_OPTIONS='--enable-source-maps'
+# Pass through the source maps toggle so run.sh can conditionally set NODE_OPTIONS.
+ARG ENABLE_SOURCE_MAPS=false
+ENV HOMARR_ENABLE_SOURCE_MAPS=$ENABLE_SOURCE_MAPS
 
 ENTRYPOINT [ "/app/entrypoint.sh" ]
 CMD ["sh", "run.sh"]