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

tests/ui/app.spec.js

@@ -348,6 +348,10 @@ test('a second person has their own feeds and their own read state', async ({ br
   const ctx = await browser.newContext();
   const page = await ctx.newPage();
   await page.goto('/login');
+  // The sign-in page shows the icon, so it has to load before anyone has signed in.
+  const icon = await page.request.get('/icon.png');
+  expect(icon.status()).toBe(200);
+  expect(icon.headers()['content-type']).toBe('image/png');
   await page.locator('#name').fill('sam');
   await page.locator('#pw').fill('sampassword');
   await page.locator('button[type=submit]').click();