Try a feed again in minutes when its host could not be looked up for the moment (#143)

205 of the Directory's 208 feeds without a category had never been read: on 2026-10-05 at 03:24
UTC every one failed with "dns error: ... Temporary failure in name resolution" within a minute,
during an outage on Tower that also stopped iPX's log reaching Loki until Tower rebooted at 11:56.
They are working podcasts, NPR's, Megaphone's, Acast's, which resolve now. A feed nobody
subscribes to is read once a day and a failing one backs off up to a day (#99), so each sat
failing, unread and so uncategorised (#117) until the next day, and explain_failure called every
DNS error "This address no longer resolves; the site is gone.", on its page and since #142 on its
Directory page. A forced check of the 208 read 205; each has its items, its description and its
own category now.

A temporary lookup failure, EAI_AGAIN, is not recorded on the feed at all: no last_error, no
error_since to back off from or call it gone by. The daemon notes it in Ctx::retry and the feed
is due again in ten minutes, which the scan's due check and the sleep until the next scan both
honour; a restart forgets it, which only makes the retry sooner. A name that does not exist is
still the feed's error, explained as "may be gone", and the Directory page, like the feed's own,
names a cause only once a feed has been failing a day; before that its last check failed.

The page also drops "Nobody here subscribes yet", which said nothing worth a line.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/configuration.md

@@ -54,7 +54,8 @@ database as described above; `download_dir`, `socket` and `organize` stay in con
 * **`schedule`** — how often feeds are re-checked. A feed's own `<ttl>` still wins when it asks to
   be polled *less* often, and a per-feed `schedule` overrides both. A feed that keeps failing
   waits as long as it has been failing before the next try, up to a day, and is back on schedule
-  after its first success. Admin-only from the UI.
+  after its first success. A moment's failure to look its host up does not count: the network, not
+  the feed, failed, and it is tried again in ten minutes. Admin-only from the UI.
 * **`organize`** — `feed` files downloads under the feed's folder; `date` under `YYYY-MM-DD`.
 * **`max_total_gb`** — the reaper deletes to get back under this, oldest first, keeping a 50 MB
   pad. Kept items are never deleted, and a file only counts as read once every subscriber has