Fix harness crash: load standalone config to skip webpack in production

The standalone next package is trimmed and doesn't include webpack.
The custom server.js was using next() which triggers config loading
that requires webpack. Fix by extracting the standalone config at
build time and setting __NEXT_PRIVATE_STANDALONE_CONFIG before
requiring next, matching what the generated standalone server does.

apps/harness/Dockerfile

@@ -25,6 +25,11 @@ COPY --from=deps /app ./
 COPY packages/db ./packages/db
 COPY apps/harness ./apps/harness
 RUN pnpm --filter @homelab/harness build
+# Extract standalone next config so the custom server can skip webpack loading
+RUN node -e "\
+  const s = require('fs').readFileSync('apps/harness/.next/standalone/apps/harness/server.js','utf8');\
+  const m = s.match(/const nextConfig = (\\{.+\\})\n/);\
+  require('fs').writeFileSync('apps/harness/.next/standalone/apps/harness/next-config.json', m[1]);"
 
 FROM base AS runner
 WORKDIR /app