Fix Next.js build failure on shared hosting (cPanel/Linux) caused by Rust/SWC thread pool 
exhaustion. The build crashes with:

  "The global thread pool has not been initialized.: ThreadPoolBuildError 
   { kind: IOError(Os { code: 11, kind: WouldBlock, message: Resource temporarily unavailable }) }
   Next.js build worker exited with code: null and signal: SIGABRT"

Root cause: Next.js 16 uses SWC (Rust compiler) which spawns a rayon thread pool. 
Shared hosting enforces a low process/thread limit (ulimit -u), causing EAGAIN (code 11) 
when SWC tries to initialize threads.

There is also a secondary webpack warning from BullMQ:
  "Critical dependency: the request of a dependency is an expression"
  from: bullmq/dist/esm/classes/child-processor.js → src/queues/index.ts → 
  src/app/api/queue/worker/route.ts

Apply ALL of the following fixes:

---

FIX 1 — Add .babelrc to disable SWC compiler (most reliable fix for shared hosting):
Create file `.babelrc` in the project root with content:
{
  "presets": ["next/babel"]
}
This forces Next.js to use Babel instead of SWC, eliminating the Rust thread pool entirely.

---

FIX 2 — Update next.config.js (or next.config.ts) to:
  a) Limit webpack parallelism to 1
  b) Externalize bullmq on server-side to fix the critical dependency warning
  c) Keep existing config (experimental.serverActions, output: 'standalone', etc.) intact

The webpack config addition should be:
  webpack: (config, { isServer }) => {
    config.parallelism = 1;
    if (isServer) {
      const existing = config.externals || [];
      config.externals = Array.isArray(existing)
        ? [...existing, 'bullmq']
        : [existing, 'bullmq'];
    }
    return config;
  }

---

FIX 3 — Update the "build" script in package.json to add environment variables 
that limit thread usage:
  "build": "RAYON_NUM_THREADS=1 NODE_OPTIONS='--max-old-space-size=512' next build"

If the project uses a custom deploy/build shell script (e.g. deploy.sh or scripts/build.sh), 
also add `export RAYON_NUM_THREADS=1` at the top of that script.

---

FIX 4 — Add RAYON_NUM_THREADS=1 to the .env file (append, do not remove existing vars):
  RAYON_NUM_THREADS=1

---

IMPORTANT CONSTRAINTS:
- Do NOT change any database schema, Prisma models, or migrations
- Do NOT modify any API routes or business logic
- Do NOT remove or alter BullMQ queue logic in src/queues/ — only externalize it from webpack
- Do NOT upgrade or downgrade any package versions
- Do NOT remove the experimental.serverActions config
- Preserve the existing output: 'standalone' setting if present in next.config.js
- After making changes, show me the final content of: .babelrc, next.config.js, and 
  the build script section of package.json

After applying all fixes, explain in one sentence what each fix does and why it helps 
on resource-constrained shared hosting.