feat: improve attachment upload interactions

[starc007]

What changed

• replace the separate image strip with consistent image attachment rows
• add compact hover previews and a shared-layout fullscreen image morph
• add full-row upload progress, success confirmation, failed uploads, retry, and pending-removal feedback
• add staggered row entrances, action tooltips, and reduced-motion handling
• expand interaction and accessibility coverage for the new states

Why

The attachment variant needed clearer upload lifecycle feedback and a more direct relationship between an image row and its full preview. These changes keep every attachment in one list while making upload, failure, retry, preview, and removal states visible.

Validation

• git diff --check
• GitHub CI required before merge

Local Bun checks are pending because the repository does not currently configure a Bun version for the normal bun command.