Accessibility: several <img> elements are missing alt text

## What happened

Several `` elements are rendered without an `alt` attribute, so screen readers announce nothing (or read the file name) for these images. This is a WCAG 2.1 **1.1.1 Non-text Content** failure.

Confirmed locations:

- `src/components/ui/ArticleCard/index.tsx` — the featured-layout image:
```tsx

```
- `src/components/ui/ArticleCard/index.tsx` — the normal-layout image:
```tsx

```
- `src/pages/features.tsx` (~line 50) — the Podman Desktop logo:
```tsx

```
- `src/pages/features.tsx` (~line 161) — the Selkie mascot image:
```tsx

```

For contrast, other images in the codebase already do this correctly (e.g. `HeroHeader`, `ThankYouSection`, `FeaturesCarousel`, `community.tsx` all pass an `alt`), so these look like oversights.

## What you expected to happen

Every meaningful `` should have a descriptive `alt` (and decorative images an empty `alt=""`), so the site is accessible to screen-reader users.

## Suggested fix

Add an `alt` to each image — e.g. `alt={props.title}` for the article cards (the thumbnail represents that article), `alt="Podman Desktop logo"` and `alt="Podman Selkie mascot"` for the two images on the features page.

I'd be happy to open a PR.

Start with the four confirmed img elements in src/components/ui/ArticleCard/index.tsx and src/pages/features.tsx, and compare them with the nearby images that already provide alt text. Add descriptive or empty alt values according to whether each image conveys information, then verify all four listed locations meet the issue's accessibility requirement.

Written by the indexing model from the issue text.