## What kind of change does this PR introduce?
- Bug fix that resolves DEPR-396
- Additional improvements to blog post image handling
## What is the current behavior?
Blog post Open Graph metadata often prefers `imgThumb` over `imgSocial`,
so social previews on X, iMessage, and similar surfaces can render the
on-site thumbnail instead of the intended social image.
The image selection and path-normalization rules are also duplicated
across blog surfaces, which makes the precedence rules easy to drift.
## What is the new behavior?
- Centralizes blog image handling in `apps/www/lib/blog-images.ts`
- Uses `imgSocial` first, then `imgThumb`, for blog OG/Twitter metadata
- Uses `imgThumb` first, then `imgSocial`, then the placeholder, for
blog thumbnails and post hero images
- Normalizes relative blog image paths into absolute URLs for metadata
- Adds warning-only validation during content reads/builds for partial
or malformed `imgSocial` / `imgThumb` config
- Updates a few recent blog posts so `imgThumb` is a thumbnail-only
asset instead of duplicating the social image
## Additional context
- Replaces #42319 with the additional above fixes
- Added unit coverage for the shared image helper
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Co-authored-by: Alan Daniel <stylesshjs@gmail.com>
