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>

CHANGELOG.md

@@ -7,6 +7,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- A feed's page in the Directory says how many people here subscribe only when someone does, without "Nobody here subscribes yet".
+
+### Fixed
+
+- A moment's DNS failure no longer marks a feed as failing for a day or calls it gone: iPX tries it again in ten minutes. One failed lookup one morning left 205 podcasts unread, uncategorised and labelled gone until the next day. A name that does not resolve is said to be maybe gone, and only once it has been failing a day, on its Directory page as on its own.
+
 ## [0.10.2] - 2026-10-05
 
 ### Fixed