Feature: Previewable URLs for data in the dataset detail page

[elainefan331]

Description:
Enable users to copy a shareable link that opens a dataset page and automatically renders a preview (3-D modal or 2-D inline plot) for a specific data.

Tasks:

• Add “Copy URL” button next to Preview for previewable data (internal & external).
• Implement URL builder
• Invoke preview:
  - Internal → choose 2-D inline vs 3-D modal based on data.
  - External → call URL-based preview flow.

Acceptance Criteria:

• “Copy URL” appears only where “Preview” appears; clicking it copies a working deep link to the clipboard and shows a confirmation toast.
• Invalid or missing preview path causes no crash; page loads normally and does not show a broken modal.
• Auto-open happens at most once per load