Cut what the audit found: dead columns, one-time upgrades, three deps

Works through TODO.md from the 2026-09-12 over-engineering audit. Drops the
entries.read/flagged/position columns (migrate() removes them from older
databases), migrate_opml_children, the legacy interval_mins key, the
contrib/ systemd units, test-only Db wrappers, a duplicate token generator,
redundant logbuf visitors, unused page state and CSS, and the infer, dirs
and tokio-stream dependencies. The icon is served once as /icon.png instead
of inlined four times, taking about 94 KB off the two pages.

The adoption's subscription half was not dead: it gives a fresh install's
first admin the config's feeds. It stays as adopt_catalogue, now tested.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TAC7sLVqfKmY6rsTLXzNgk

CHANGELOG.md

@@ -36,6 +36,17 @@ The long form, with what was wrong before and how it was found, is in
 - Export and Import in Settings say what they do.
 - The sign-in page shows the original icon large.
 - Nothing animates when your system asks for reduced motion.
+- The pages are about 90 KB smaller: the icon is served once instead of written into each.
+- A web token generated for a new install is 64 characters instead of 32.
+
+### Removed
+
+- The systemd units in `contrib/`. Run ipx with Docker, or point a unit of your own at
+  `ipx daemon`.
+- Upgrading from before 0.3.0 directly: what was read, kept or part-played before accounts is no
+  longer carried over to the admin, and OPML feeds that old versions wrote into `config.toml` are
+  no longer moved out of it. Upgrade through 0.4.0 first.
+- `interval_mins` in `config.toml` is ignored; use `schedule`.
 
 ### Fixed