docs: update detection core with tips for using Gemini integration

[tberends]

Description

On request of @SkalskiP at PR: https://github.com/roboflow/notebooks/pull/384

This PR improves the documentation regarding the ordering of content in requests that combine images with text prompts. Following Google's Gemini API best practices, text prompts are now placed after image parts in the contents array when using a single image with text.

Type of change

• This change requires a documentation update

How has this change been tested, please provide a testcase or example of how you tested the change?

According to the Gemini API documentation on image prompts, when using a single image with text, the recommended approach is to place the text prompt after the image part in the contents array. This ordering has been shown to produce significantly better results in practice.

In our testing with Process & Instrument Diagrams (P&IDs) using object detection, this reordering led to drastically improved accuracy in bounding box positioning. While the object labels were already accurate, the spatial precision of detected elements improved considerably with the optimized prompt ordering

Docs

• Docs updated? What were the changes: updated the tips for prompt engineering

[Copilot]

Pull request overview

Updates Detections.from_lmm() / Detections.from_vlm() documentation to add Gemini-specific prompt engineering tips, emphasizing best-practice ordering for mixed image+text requests.

Changes:

• Added a “Prompt engineering” tip block for Gemini 2.0 describing normalized box coordinates and recommended prompt guidance.
• Added a note for Gemini 2.5 about placing the text prompt after the image part in the contents array for single-image prompts.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72%. Comparing base (0ebab21) to head (47c0773).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

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  Coverage       72%     72%           
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  Files           61      61           
  Lines         7245    7245           
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  Hits          5242    5242           
  Misses        2003    2003           

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