Fix the open bugs: read state, Unread tab, feed errors, theme button, log button, relative images

- Opening an item stays read: a list refresh that crossed with the write no longer
  puts the unread dot back (#16).
- On the Unread tab the item you were reading goes when you move to the next (#17).
- Feed errors mark the feed with a red ! instead of a toast per failure (#20).
- The theme is chosen in Settings only (#15).
- The server leaves the Log button out of a non-admin's page, so it no longer flashes (#29).
- Relative images and links in a post resolve against the post's link (#28).

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

CHANGELOG.md

@@ -10,6 +10,23 @@ The long form, with what was wrong before and how it was found, is in
 
 ## [Unreleased]
 
+### Changed
+
+- A feed that fails to check gets a red ! in the feed list, and its page says why, in place of a
+  pop-up per failure that everyone saw during a scan of every feed.
+- The theme is chosen in Settings only; the button beside the iPodderX name is gone.
+
+### Fixed
+
+- An item you open stays read. A list refresh that crossed with marking it read could put its
+  unread dot back until the next refresh.
+- On the Unread tab, the item you were reading leaves the list as soon as you move to the next
+  one, rather than a few read items lingering until a refresh cleared them.
+- The Log button no longer shows for a moment on every load for anyone but an admin; the server
+  leaves it out of their page.
+- An image or link in a post given relative to the post, such as The Observation Deck's, now
+  points at the post's site rather than at ipx, and shows.
+
 ## [0.6.1] - 2026-09-15
 
 ### Fixed