Fix dead brand fallback, add best-effort size parsing

Root-caused the brand/size/condition gaps by comparing the raw HTML
the bookmarklet actually fetches (pre-hydration server response)
against the live, client-hydrated page:

- The breadcrumbLink fallback for brand was dead code - Depop's
  breadcrumb nav is rendered client-side only and never appears in
  the raw fetch() response (confirmed: 0 breadcrumb links in the raw
  HTML on every listing checked). Brand now only comes from the
  linkAttribute link, which the raw HTML does contain when an item
  has a real tagged brand - blank is correct for "Other"/unbranded
  items, not a bug.
- Condition genuinely isn't present as structured data on these
  product pages at all (confirmed via direct search for Depop's known
  condition vocabulary - zero matches). Left blank rather than
  guessing at something that isn't there.
- Size is usually spelled out in the seller's own title text ("size
  extra large", "size medium"), so added a regex to pull it out of
  the description as a best-effort value.

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