feat(detail): collapse attachments when count exceeds 2

[bartekmp]

Summary

• When an email has more than 2 attachments, replaces the flat list with a collapsed summary row showing the attachment count and up to 3 file-type chips (e.g. PDF, PNG, DOCX) sorted by frequency
• Clicking the summary row expands a fixed-height (160 px) scrollable list of all attachment items — same download behaviour as before
• Clicking the summary again collapses the list; chevron animates between ▶ (collapsed) and ▼ (expanded)
• Emails with ≤ 2 attachments are unaffected

Test plan

• Open an email with 1–2 attachments → flat list renders as before, no summary row
• Open an email with 3+ attachments → summary row shows count + type chips, list is hidden
• Click summary row → list expands, chevron points down, aria-expanded becomes true
• Scroll within the expanded list when there are many attachments (max-height 160 px)
• Click a file in the expanded list → download triggers correctly
• Click summary row again → list collapses, chevron points right
• Verify type chips reflect the most common extensions (e.g. 3 PDFs + 1 PNG → PDF chip first)

https://claude.ai/code/session_011k8zuM3FhFRooN1fpGYhNi

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Generated by Claude Code

[Copilot]

Pull request overview

Adds a collapsed/expandable attachments UI in the email detail view when an email has more than two attachments, while keeping the existing flat list behavior for 1–2 attachments.

Changes:

• Refactors attachment row creation into a helper and introduces a collapsible “attachment summary” row for 3+ attachments.
• Adds new CSS for the attachment summary row, type chips, chevron animation, and a max-height scrollable expanded list.
• Updates package-lock.json with platform-metadata changes (unrelated to the UI feature).

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
src/popup/popup.css	Adds styling for the new attachment summary row, type chips, chevron, and scrollable expanded list.
src/popup/detail.js	Implements the collapsed/expandable attachment list behavior and extracts attachment item rendering into a helper.
package-lock.json	Removes libc metadata from several Rollup platform optional packages (scope unrelated to this feature).

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