Fix prod frontend container: tsx on PATH and cap build heap

Runner stage was invoking `tsx server.ts` via sh, which doesn't
have node_modules/.bin on PATH, so the container crash-looped with
"tsx: not found" (502 at the edge). Use the absolute binary path
instead.

Also caps the Vite build's V8 heap to 1.5 GB so a future build on
the 4-core / 8 GB VPS can't OOM-kill neighbouring services.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/Dockerfile

@@ -21,6 +21,8 @@ FROM node:22-alpine AS builder
 WORKDIR /app
 COPY --from=deps /app/node_modules ./node_modules
 COPY . .
+# Cap node heap so a build on a small VPS can't OOM-kill neighbours.
+ENV NODE_OPTIONS=--max-old-space-size=1536
 RUN corepack enable && pnpm build
 
 # Production: Hono serves dist/ + /api/copilotkit on port 3000
@@ -34,4 +36,4 @@ COPY server.ts package.json ./
 EXPOSE 3000
 HEALTHCHECK --interval=30s --timeout=3s --retries=3 \
   CMD wget -qO- http://127.0.0.1:3000/api/health || exit 1
-CMD ["sh", "-c", "corepack enable && tsx server.ts"]
+CMD ["./node_modules/.bin/tsx", "server.ts"]