Add image grid layout for plugin README content

[simonhamp]

Summary

• Styles <p> tags containing images in plugin README prose content as a responsive grid
• 1 column on mobile, 2 on sm, 3 on lg, with gap-4 spacing
• Removes box shadow from images within the grid for a cleaner look

Test plan

• Visit a plugin page with multiple images in a <p> tag (e.g. /plugins/srwiez/nativephp-mobile-screenshots)
• Verify images display in a grid with up to 3 columns on large screens
• Verify responsive behaviour: 1 col on mobile, 2 on sm, 3 on lg
• Verify single-image <p> tags still render correctly
• Verify non-image prose content is unaffected

🤖 Generated with Claude Code