[YashAnand69]

An unsuccessful export-ID request sets an error message, then returns normally and lets the form close the dialog. Keep failures in the form's error path so the message stays visible and Download can be retried. Close the dialog after a successful export.

Fixes #874.

Validation:

• Actual Chrome/JBrowse/Apollo flow on Linux: all three export tests pass, including error → visible message → retry. On unchanged main, the new case fails because the dialog disappears; the existing FASTA and GFF-only downloads both pass. The new case intercepts only the export-ID response and stubs the retry's new window; the existing cases download and check actual files. Browser validation.
• 54 local plugin unit tests and 11 snapshots pass; plugin TypeScript, changed-file ESLint, formatting and normal commit hooks pass.
• The upstream strict lint and configuration type-check jobs pass on Ubuntu. Lint validation. Full repository lint locally reports identical type-resolution errors on untouched main and this patch; no suppression or unrelated fixes are included.

The temporary validation workflows remain on fork-only branches. The current #863 and #839 versions retain this same error/close behavior; this patch changes neither their account/assembly architecture nor the export format.

AI assistance: OpenAI Codex investigated, implemented, tested and reviewed this change.