Fixes to the "See it on your own product" demo landing

A round of fixes to the demo submission landing: no more 500 error screens for real users hit by the anti-bot system, a readable mail sender, and admin material import that surfaces the photos under Products as well, not only Packshots.

Five issues reported after the first round of using the demo landing have been addressed in a single release. Real prospects who happen to be incorrectly flagged by our anti-bot system will no longer see a 500 error screen when trying to upload photos — the wizard behaves as it did before, and an ordinary network-style error message is shown that can simply be retried. The sender shown on the confirmation and follow-up emails now displays as a configurable display name (for example "Qamera AI") instead of just the local part of the address.

On the operator side, the "Import materials" action now also creates a single Airtable Products record per submission and links the imported photos to it. Imported photos therefore appear in both the Packshots tab and the Products tab in the Qamera workspace right away, which unblocks Prepare Photos and Photo Shoot. The operation is idempotent — re-running import on the same submission will not duplicate either the Product or its Images.

The admin panel also gets two small but long-overdue improvements: a new "Demo Submissions" entry in the sidebar (the page existed but was not discoverable from the menu) and a "Go to team" button on the submission detail view that links directly to the workspace of the created demo account.