Fix env var name mismatch: NODE_RENDERER_CONCURRENCY → RENDERER_WORKERS_COUNT

The launcher was reading NODE_RENDERER_CONCURRENCY (inherited from
PR #723's f55dcc2), but app.yml sets RENDERER_WORKERS_COUNT (canonical
per marketplace + Pro renderer library). Result: prod/staging would
ignore the deployed value and always use the launcher default.

RENDERER_WORKERS_COUNT is the canonical env var name per:
- docs/oss/building-features/node-renderer/js-configuration.md
  "workersCount (default: process.env.RENDERER_WORKERS_COUNT ...)"
- packages/react-on-rails-pro-node-renderer/src/shared/configBuilder.ts:200
  "workersCount: env.RENDERER_WORKERS_COUNT ? parseInt(...) : defaultWorkersCount()"
- react-server-components-marketplace-demo/node-renderer.js

NODE_RENDERER_CONCURRENCY was a non-canonical name invented by PR #723.

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

Author: ihabadham

renderer/node-renderer.js

@@ -33,7 +33,7 @@ const config = {
   password: rendererPassword,
   port: parseIntegerEnv('RENDERER_PORT', 3800, { min: 1, max: 65535 }),
   supportModules: true,
-  workersCount: parseIntegerEnv('NODE_RENDERER_CONCURRENCY', 3, { min: 0 }),
+  workersCount: parseIntegerEnv('RENDERER_WORKERS_COUNT', 3, { min: 0 }),
   // Expose globals the VM sandbox doesn't auto-provide but that downstream
   // deps rely on during SSR. Without URL, react-router-dom's NavLink throws
   // `ReferenceError: URL is not defined` via encodeLocation.
@@ -42,7 +42,7 @@ const config = {
 
 // CI hosts report more CPUs than allocated to the container; cap workers to
 // avoid oversubscribing memory.
-if (process.env.CI && process.env.NODE_RENDERER_CONCURRENCY == null) {
+if (process.env.CI && process.env.RENDERER_WORKERS_COUNT == null) {
   config.workersCount = 2;
 }