docs(extraction): Page Elements NIM image size limits and NVCF assets API (NVBug 5456115)

[kheiss-uwzoo]

Summary

• Document hosted Page Elements (and related object-detection) NIM inline base64 limit (~180,000 characters) and the NVCF Asset API workflow for oversized images (NVBug 5456115).
• Add canonical guidance in troubleshoot.md with limits table, NRL pipeline behavior, and a Python upload + infer example.
• Cross-link from api-keys.md and multimodal-extraction.md so build.nvidia.com integrators can find the workflow.

NVBugs

5456115 — Page Elements NIM image size limits and assets API documentation gap

Test plan

• .\.cursor\scripts\check-nrl-doc-leakage.ps1 passes on this branch
• Review anchor troubleshoot.md#hosted-page-elements-nim-image-size-limits renders in MkDocs preview
• Verify external links resolve (Object Detection NIM API reference, NVCF Create Asset, NVCF assets user guide)

Follow-up (out of scope for this docs PR)

• Eng: Align NRL remote Page Elements client max payload with hosted 180K cap (yolox.py uses 512K today).
• NIM docs: Update Object Detection API reference troubleshooting + OpenAPI on docs.nvidia.com/nim/ingestion/object-detection/.