Open a live progress tab immediately when the bookmarklet is clicked

Previously nothing visible happened until the entire scrape finished
(which can now take a while since fetches are throttled one-at-a-time).
Now:

- Both bookmarklets open a named window (window.open(..., 'depopVintedResults'))
  as their very first action - synchronous, direct response to the
  click, so popup blockers allow it same as a normal user-triggered
  popup.
- As each item is read, they postMessage a progress update (X of Y)
  and the extracted item to that window, which appends a live preview
  card and fills in a progress bar (new /progress route + template).
- The final results submission now targets that same named window
  instead of the current tab, so it seamlessly replaces the progress
  view with the real formatted-drafts page once done - the original
  shop/closet tab is left untouched throughout.

Verified the receiving side (progress.html's message listener: bar,
counter, live cards) directly with synthetic postMessage calls - it's
correct. Could not fully verify the two-independent-tabs behavior of
window.open end-to-end in the sandboxed browser tool used for testing
here, since it collapses window.open into a same-tab navigation
(same quirk hit earlier with target="_blank") - window.open with a
name, called synchronously from a click, is standard/reliable browser
behavior, but this specific part needs real-browser confirmation.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>