test: drive the Settings screen in a browser and guard every popup element id (closes #229)

Nothing exercised the Settings view in a browser, and jest runs in the
node environment with no DOM, so the densest run of $("...") lookups in
the codebase was unverified at runtime. A wrong id is valid JavaScript
naming a defined function: $() returns null and the next property access
throws, which inside a view's init() aborts the rest of the popup's
init() and leaves every screen blank.

Two halves, because they catch different things.

The e2e suite (tests/e2e/run.js) gains six cases between the address
removal and dust threshold sections. They assert the About well and the
wallet list were actually written — show() populates those last, so
reading them back proves the whole of show() ran rather than just enough
of it to unhide the section — that the four Token Spam Protection
controls are real input[type=checkbox] elements defaulted on, and that
the theme and network selectors offer exactly the choices
src/shared/networks.js and index.html define while carrying the
persisted value. One filter is then toggled off and back on across a
popup reopen each way, which runs the change handler, saveState(),
loadState() and the init() assignment rather than only looking at the
screen. Each group records a coverage key and a final case demands the
exact set, so a section that silently stopped running reddens the suite
instead of shrinking it.

tests/popupElementIds.test.js is the general half and needs no browser,
so jest picks it up and it runs in make check: every literal id reached
through $(), document.getElementById(), showError()/hideError() and
showView() must exist in src/popup/index.html, no id in index.html may
be defined twice, and the scan asserts it found the code and the markup
so it cannot pass by covering nothing. Only literal arguments are
resolvable statically; $(containerId) and a lookup naming the wrong
existing element are the browser suites' job, and README says so.

Demonstrated against three deliberate breaks. A typo'd id in
settings.js reddens both halves, the e2e run reporting
"pageerror: Cannot set properties of null (setting 'checked')" against
its first test. A handler bound to the wrong but existing element passes
the static guard and reddens only the new functional case. A typo in a
view no browser suite opens reddens only the static guard.

TODO.md

@@ -45,6 +45,27 @@ undefined identifiers, which is how
 
 # Completed Steps
 
+- 2026-08-17: The Settings screen is driven in a browser, and every element id
+  the popup looks up is checked statically. Nothing exercised Settings in the
+  e2e suite, and jest runs with no DOM, so the densest run of `$("...")` lookups
+  in the codebase was unverified at runtime. Six new cases in `tests/e2e/run.js`
+  reach Settings, assert the About well and the wallet list were actually
+  written, assert the four Token Spam Protection checkboxes are real checkboxes
+  defaulted on, assert the theme and network selectors offer the choices
+  `src/shared/networks.js` defines and carry the persisted value, and toggle one
+  filter off and back on across a popup reopen each way — which runs the change
+  handler, `saveState()`, `loadState()` and the `init()` assignment rather than
+  just looking at the screen. Each group records a coverage key and a final case
+  demands the exact set, so a shortened or skipped section reddens the run
+  instead of shrinking it. `tests/popupElementIds.test.js` is the general half
+  and runs in `make check` with no browser: every literal id reached through
+  `$()`, `document.getElementById()`, `showError()`/`hideError()` and
+  `showView()` must exist in `src/popup/index.html`, which no id in `index.html`
+  may define twice. Demonstrated on three deliberate breaks — a typo'd id (both
+  halves red), a handler bound to the wrong but existing element (only the
+  functional e2e case red), and a typo in a view no browser suite opens (only
+  the static guard red)
+  ([#229](https://git.eeqj.de/sneak/AutistMask/issues/229)).
 - 2026-08-17: `README.md` no longer advertises a defect the wallet does not
   have. The End-to-End Tests section listed the EIP-1193 code being dropped in
   the last hop into the page as a standing limit of the dApp coverage; that