[DwC export]: Add "Copy RSS Feed URL" button to Update RSS Feed notification

[grantfitzsimmons]

Goal

After triggering an RSS feed update, the result notification must include a one-click button to copy the RSS feed endpoint URL to the clipboard.

Background

Institutions need to share their RSS feed URL with aggregators. A one-click copy button in the update notification reduces friction.

Acceptance Criteria

• The post-update notification includes a Copy RSS Feed URL button.
• Clicking it copies the full RSS feed endpoint URL to the clipboard.
• A confirmation tooltip (e.g., "Copied!") is shown after clicking.
• The RSS feed URL points to the correct Specify endpoint for the institution's feed.