ci: run the web UI DOM test suites; fix two stale suites (#660)

A new "Web UI JS tests" job installs jsdom, starts the web interface in
emulator mode and runs test/js/run_all.js with REQUIRE_DOM=1, which makes a
DOM suite that can't run a failure rather than a silent skip. (The unit
suites were already covered through pytest.)

Two suites failed against main when run for real:
- test_tools_sections rendered the Tools partial without LEDEscape, which
  base.html's app-early.js defines; it now installs it in beforeParse, and
  supplies two sample Starlark apps (one id with a quote) when the server
  has none, instead of assuming a device with apps and Pixlet.
- test_store_dom assumed the live registry had at most 48 plugins; it now
  checks pagination whichever side of 48 it is.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

test/js/dom/test_tools_sections.js

@@ -12,6 +12,19 @@ const get = p => new Promise((res, rej) =>
   const partial = await get('/partials/tools');
   const bridge = JSON.parse(await get('/api/v3/integrations/mqtt-bridge'));
   const apps = JSON.parse(await get('/api/v3/starlark/editor/apps'));
+  // A dev box or CI runner has no Starlark apps and no Pixlet binary, which
+  // leaves the editor section with nothing to render. Keep the real payload's
+  // shape but give it two apps -- one id carrying a quote, which is what the
+  // dataset (not inline onclick) check below exists to catch.
+  if (!(apps.data && apps.data.apps && apps.data.apps.length)) {
+    apps.data = Object.assign({}, apps.data, {
+      pixlet_available: true,
+      apps: [
+        { id: 'clock-demo', name: 'Clock demo', editable: true },
+        { id: "it's-quoted", name: 'Quoted id', editable: true },
+      ],
+    });
+  }
 
   const errs = [];
   const vc = new VirtualConsole();
@@ -37,7 +50,13 @@ const get = p => new Promise((res, rej) =>
   // and the page fails in ways it never would in a browser.
   const dom = new JSDOM(`<!doctype html><html><body>${partial}</body></html>`,
     { runScripts: 'dangerously', virtualConsole: vc, url: BASE + '/',
-      beforeParse(w) { w.fetch = stubFetch; w.confirm = () => true; } });
+      beforeParse(w) {
+        w.fetch = stubFetch; w.confirm = () => true;
+        // The partial runs inside base.html, which defines LEDEscape (in
+        // app-early.js) before any tab loads; rendered on its own it needs it
+        // installed the same way.
+        require('../led_escape').install(w);
+      } });
   const { window } = dom;
 
   const tick = ms => new Promise(r => setTimeout(r, ms));