feat(lightbox): support zoom and refine close button layout

[yonzilch]

Motivation

Current lightbox lacks zoom support, limiting users' ability to inspect image
content closely. Additionally, the lightbox-close button's current position
and size looks not good enough.

Expected behavior

• Users can zoom in/out when viewing content in the lightbox
• The lightbox-close button is easier to access and visually aligned with the lightbox layout
• The close button does not overlap key content or interfere with zoom interactions

Scope

Included:

• Implement zoom behavior for lightbox content
• Update lightbox-close styling and placement
• Ensure responsive behavior across common screen sizes

Out of scope:

• keyboard shortcuts zoom
• zoom persistence across sessions

Acceptance criteria

• Zoom works reliably in the lightbox
• lightbox-close is clearly visible and appropriately sized
• Button placement remains consistent on desktop and mobile
• No regression to existing open/close behavior

Risks or constraints

None identified at this time.