Docs: General documentation updates / fixes

[Copilot]

The docs included a standalone section for loading a custom layout model as the default layout_predictor, which duplicated/overlapped guidance and created confusion in the custom-model workflow. This PR removes that redundant block and keeps the OCR pipeline integration path as the canonical example.

• What changed

  • Removed the section “Load a custom layout analysis model trained on another set of classes as the default one” from:
    • docs/source/using_doctr/custom_models_training.rst
  • Kept the existing OCR integration example (ocr_predictor(..., detect_layout=True, layout_arch=layout_model)) and surrounding custom-model sections intact.

• Resulting documentation flow

  • Recognition customization example
  • Layout customization through OCR pipeline (single recommended path)
  • KIE/custom preprocessor examples

layout_model = lw_detr_s(pretrained=False, class_names=["heading", "paragraph", "figure", "table"])
layout_model.from_pretrained("<path_to_pt>")

predictor = ocr_predictor(pretrained=True, detect_layout=True, layout_arch=layout_model)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.94%. Comparing base (3d5ca38) to head (b5d0262).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2080      +/-   ##
==========================================
+ Coverage   96.89%   96.94%   +0.05%     
==========================================
  Files         156      156              
  Lines        7535     7535              
==========================================
+ Hits         7301     7305       +4     
+ Misses        234      230       -4     

Flag	Coverage Δ
unittests	96.94% <100.00%> (+0.05%)	⬆️

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