[unjica]

Refs #853 #854 #855

Docs only, verified against packages/telemetry-node and telemetry-core on develop.

• Node docs: ingest URL fallback differs between /docs/node and /error-tracking/nodejs #853: /docs/node now uses the shared nodeSetup snippet, so both pages show the same fallback (HOSTED_API_URL). Both state that ingestUrl is required and the SDK has no built-in default (TelemetryConfig.ingestUrl: string).
• Node docs: add CommonJS (require) guidance #854: package.json for node and core is "type": "module" with only an "import" export condition, so require() is NOT claimed. Documented as ESM-only, with a dynamic import() example for CommonJS callers that awaits flush() inside an async function.
• Node docs: add Express error handler example #855: Express error-handling middleware example using trackError(err, context) + next(err), on both pages.
  Short-jobs/flush section untouched (TT-024: Node SDK flush() doesn't wait for handled trackError(), so a job's error is lost when it calls process.exit() after await flush() #851 covers it).