fix: revert production source maps to restore v1.67.0 memory baseline

CodeRabbit review addressed:
- Removed the env-var gating (simpler: just remove source maps entirely)
- CI health check now fails fast if container never becomes healthy

Changes vs origin/main:
- next.config.ts: remove productionBrowserSourceMaps and serverSourceMaps
  (they default to false, restoring pre-v1.68.0 behavior)
- Dockerfile: remove .map copy step and NODE_OPTIONS=--enable-source-maps
- CI: add memory-regression job (<700MB guardrail)

Closes #6123

scripts/run.sh

@@ -58,12 +58,6 @@ terminate() {
 
 trap terminate TERM INT
 
-# Enable source maps in Node.js when explicitly opted in.
-# Default off — see https://github.com/homarr-labs/homarr/issues/6123
-if [ "${HOMARR_ENABLE_SOURCE_MAPS}" = "true" ]; then
-  export NODE_OPTIONS="--enable-source-maps${NODE_OPTIONS:+ $NODE_OPTIONS}"
-fi
-
 node apps/nextjs/server.js &
 NEXTJS_PID=$!