v0.1.2 — walk the sitemap newest-first

Fixes --mode offer coming back empty on a site that is serving
perfectly. If a small offer run gave you zero rows, this is that.

The canary found it — the second thing it has found in two runs, which is
what a canary that is not gated on a secret is for.

justjoin.it serves sitemaps/active-jobs/part0.xml oldest first (its
first lastmod was 2026-09-14 and its last 2026-09-18) and generates it
ahead of any fetch, so its head is where offers that have since been taken
down collect. Measured by asking the endpoint for a sample of each end:

sample	alive	gone
first 12 entries	10	2
last 12 entries	12	0
12 at random	12	0

So --mode offer --pages 3 was being pointed at the three likeliest-dead
addresses in the file.

The enumeration is now sorted by lastmod descending — which is also what
--pages N should have meant all along: the N most recently updated
offers, not the N most stale. Entries with no lastmod are kept and sort
last rather than being dropped, and the document order is still available
so a check can assert the sort loses nothing.

The offer canary asks for five offers rather than three, so one delisted
offer is an ordinary event rather than a red check — while zero rows out of
five still means something real broke.

591 offline checks, up from 586.