Prepend and dedupe attachments

[firewalker06]

Summary

• Dedupe saved attachments by normalized URL/path target instead of title-sensitive identity.
• Store newly added attachment records first so flyouts show the latest attachments at the top.
• Prepend pending Remote UI uploads and skip repeated browser files before sending.

Verification

• bin/test
• node --check lib/hq/remote_ui/assets/app.js
• git diff --check
• Isolated headless Chrome check for Remote UI attachment dedupe/prepend behavior.