Fix missing image alt text and intrinsic dimensions

## Why this needs addressing

The live homepage contains 24 images; 3 news thumbnails have no `alt` attribute. Nearly all sampled images also lack intrinsic `width`/`height` attributes. This is a confirmed accessibility gap and can contribute to layout shifts while images load.

## Requested change

- Give meaningful content images concise, context-appropriate alt text.
- Use `alt=""` only for genuinely decorative images.
- Add intrinsic dimensions or an equivalent aspect-ratio reservation for stable images, especially above the fold and repeated card components.
- Audit shared image partials as well as homepage content so the fix is template-level.

## Acceptance criteria

- No indexable/content image is missing an alt decision (meaningful alt or deliberate empty alt).
- Representative pages reserve image space before loading and show no avoidable layout shift.
- Existing responsive sizing and lazy loading continue to work.