fix(portal-bff): use bracket notation for process.env access

The strict-TS option noPropertyAccessFromIndexSignature: true (set in
tsconfig.base.json per ADR-0004) forbids dot-notation access on index
signatures. process.env is typed as { [key: string]: string | undefined }
so process.env.PORT must be written process.env['PORT']. The Nx
generator wrote the dot form by default; fix to comply with the
project's strict-TS bar.

Touched: portal-bff main.ts and the three portal-bff-e2e support files
(global-setup, global-teardown, test-setup).

apps/portal-bff-e2e/src/support/global-teardown.ts

@@ -4,7 +4,7 @@ import { killPort } from '@nx/node/utils';
 module.exports = async function () {
   // Put clean up logic here (e.g. stopping services, docker-compose, etc.).
   // Hint: `globalThis` is shared between setup and teardown.
-  const port = process.env.PORT ? Number(process.env.PORT) : 3000;
+  const port = process.env['PORT'] ? Number(process.env['PORT']) : 3000;
   await killPort(port);
   console.log(globalThis.__TEARDOWN_MESSAGE__);
 };