Reuse image popup for chat and workspace images

[paullizer]

Summary

Reuse the New Features/Admin image popup pattern for viewing generated, uploaded, and workspace images in chat.

User Value

Tracking this as a GitHub issue moves the backlog item out of a private markdown file and gives the team a clear place to prioritize, design, implement, and validate the work.

Proposed Behavior

Support keyboard controls, mobile sizing, blob-backed authorization, and images embedded in exports or proposal cards.

Acceptance Criteria

• The requested behavior is designed or implemented for the relevant SimpleChat surfaces.
• Permission, configuration, and existing-feature interactions are accounted for.
• Tests, documentation, or validation notes are added as appropriate.

Notes

• Source backlog entry: Reuse Image Popup For Chat And Workspace Images
• Source file: priv-simplechat-2/grouped_feature_fix_backlog.md
• Backlog status: Extension
• Current anchors: image proposal cards, enhanced citations/image previews, workspace document viewers
• Proposed roadmap priority: P2
• Proposed roadmap size: M