Fix the UI dying at load, and add a page smoke test

$('#prefs').onclick referenced a prefsModal that was never defined, and an
uncaught ReferenceError stops the whole script -- taking the theme toggle,
the feed filter, the event stream and loadFeeds() down with it, so the app
rendered an empty shell.

The scheduling patch had anchored on a function the rewrite already
deleted; str.replace matched nothing and said nothing.

tests/page-smoke.js executes the page against a stub DOM so this class of
failure is visible, since every server-side check passed while the UI was
completely dead. Handler wiring now skips a bad reference instead of
throwing.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AdXho5tTkjFLeUXKbEjKBh

PROGRESS.md

@@ -56,6 +56,36 @@ and until now nothing set them.
 
 ---
 
+## 2026-09-10 — The whole UI was dead, and server-side tests could not see it
+
+Reported as "my feeds seem to have disappeared", then "settings and dark/light mode don't do
+anything either". One cause for all three.
+
+`$('#prefs').onclick = prefsModal` referenced a function that did not exist. An uncaught
+`ReferenceError` stops the entire script, and that line sits above the theme toggle, the feed
+filter, the SSE connection and the `loadFeeds()` call that fills the sidebar — so everything below
+it silently never ran.
+
+**Cause: a patch anchored on something already deleted.** The scheduling UI was inserted with
+`str.replace` anchored on `function toggleSettings(){`, which belonged to the *old* basic UI that
+the full rewrite had already removed. Python's replace matches nothing and says nothing, and there
+was no assert — so `prefsModal`, `everyText`, `due` and `globalEvery` were never added, while the
+line *calling* `prefsModal` went in fine via a different anchor that did match.
+
+**Why it got through.** Every check was server-side: curl for status codes, JSON shape, config
+contents. All passed, because the server was fine. `node --check` also passed — it parses, and a
+ReferenceError is a runtime failure. The page was never executed.
+
+`tests/page-smoke.js` now runs the real page script against a stub DOM, fails on anything thrown,
+and flags handlers wired to elements that do not exist. Confirmed non-vacuous by reintroducing the
+exact bug: exit 1 pointing at the offending line, clean once restored. Run it with
+`node tests/page-smoke.js`.
+
+Wiring is also defensive now — `on(sel, ev, fn)` logs and skips rather than throwing, so one dead
+reference cannot blank the app again.
+
+---
+
 ## 2026-09-10 — Scheduling, and two bugs it uncovered
 
 **Scheduling.** The original engine had none — it only skipped feeds on `<ttl>`; the schedule lived