fix(media): downsample oversized image model inputs

[MaojiaSheng]

Description

Keep imported image resources unchanged while avoiding provider-side multimodal embedding failures for oversized images. The embedding path now builds a temporary downsampled image data URI when image bytes exceed the shared large-image limits.

Move reusable image size thresholds into media_limits so both parser-side large image handling and embedding-side input preparation depend on a common utility instead of embedding_utils importing parser internals.

Add vectorize_file coverage confirming large image embedding inputs are resized and the stored resource bytes are preserved.

Human Involvement

• A human participated in the implementation or review loop
• This PR was generated entirely by AI agents without human participation in the loop

Related Issue

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

• Add shared image model-input preparation in openviking/utils/image_search.py
  • Detects oversized images using the existing large-image limits
  • Downsamples image bytes in memory for model calls
  • Leaves stored resource bytes unchanged
• Apply the shared downsampling path to semantic image summary generation
  • Prevents generate_image_summary() from sending oversized raw image bytes to VLM providers
• Apply the same shared downsampling path to image embedding inputs
  • Keeps embedding_utils.py from owning parser/media-specific resizing logic
• Add test coverage for VLM image summaries
  • Verifies model input is resized
  • Verifies original stored bytes are preserved

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

Additional Notes