[WEB-5827] fix: persist external cover image URLs (Unsplash) in project updates

[anmolsinghbhatia]

Problem

When selecting an Unsplash image (or any external URL) as a project cover image, the URL wasn't being saved to the backend. The handleCoverImageChange function was returning null for external URLs, causing the update payload to exclude the cover image.

Root Cause

The handleCoverImageChange function only returned a payload for:

1. Image removal (returns null values)
2. Local static images that need upload (for user assets only)

External URLs like Unsplash images are classified as "uploaded_asset" type and don't require upload, so the function fell through to return null, preventing the URL from being included in the update payload.

Solution

• Updated handleCoverImageChange to return the cover image URL in the payload for external/uploaded assets
• Replaced cover_image_url with cover_image fields

Testing

• [x] Verify Unsplash images are saved when selected in project form
• [x] Verify local static images still upload correctly
• [x] Verify image removal still works correctly
• [x] Verify no regressions in existing cover image functionality

Summary by CodeRabbit

• Bug Fixes
  • Improved cover image handling for uploaded and external assets to ensure consistent processing across all asset types.

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