Add Extract materials action to model contextual menu

[Gopmyc]

Description

This PR adds an Extract materials action to the model contextual menu in the Asset Browser.

When used on a model asset, the editor now:

• Resolves embedded materials from the selected model
• Saves each embedded material as a standalone .ovmat file next to the model
• Uses unique file paths to avoid overwriting existing files
• Refreshes the Asset Browser list via existing duplicate notifications

This provides a direct way to extract embedded materials and edit them as regular material assets.

Related Issue(s)

Fixes #764

Review Guidance

• In the Asset Browser, right-click a model file.
• Confirm the new Extract materials entry is present in the contextual menu.
• Click Extract materials.
• Verify .ovmat files are created next to the model (one per extracted embedded material).
• Verify existing files are not overwritten (unique naming is applied).

Screenshots/GIFs

N/A

AI Usage Disclosure

Generated new code

Checklist

• My code follows the project's code style guidelines
• When applicable, I have commented my code, particularly in hard-to-understand areas
• When applicable, I have updated the documentation accordingly
• My changes don't generate new warnings or errors
• I have reviewed and take responsibility for all code in this PR (including any AI-assisted contributions)