Favicon storage/loading issues addressed

Settings Cancel fixed. Cancel is now an explicit non-submit button, so invalid form fields can't trap the dialog open. I made the same correction to Restore.
Size-field validation fixed. The 1 GB value in your screenshot was technically invalid because of the previous min/step combination—that's why Firefox suggested bizarre values like 0.901 and 1.01.
Added a Stats button and Domain Statistics interface. It shows each exact hostname's page count, Text (Chars), estimated archive size, and percentage of the overall archive.
Domain Stats is sortable and searchable, with multi-selection.
Blacklist selected adds selected domains to the blacklist. As before, blacklisting does not destroy existing archive data.
Purge selected removes existing records for those selected hostnames. It uses the hostname index rather than scanning page text.
Blacklisted domains are marked Blocked in the stats view.
Main archive heading changed from Text → Text (Chars).
Removed the redundant ch suffix from displayed values.
Added best-effort favicons beside entries and domains. This uses Firefox's internal page-icon: favicon cache rather than an external favicon service; Firefox documents that scheme as loading favicons already stored by its favicon service. If Zen refuses the internal scheme from an extension page, the icon simply disappears and the row falls back to the existing text-only presentation.

Changes in this release:

Added individual and multi-select deletion of archived entries.
Added “Delete matching” for removing all records matching the current search and/or domain filter.
Added a domain blacklist. Blacklisted domains are checked before page text is extracted, so excluded pages are not archived.
Added optional retention controls based on maximum archive age and maximum logical archive size. Both are disabled by default.
Added domain filtering to the archive interface.
Improved archive-size accounting and moved large filtering/deletion operations into Web Workers to keep the UI responsive with large databases.
IndexedDB schema was updated from v3 to v4. Existing archive records are retained during the upgrade.