fix: the Chrome layout tests and popup comments use the popup's real 396x600 size (closes #556)

POPUP_VIEWPORT in tests/e2e/run.js said 360x600, while body in
src/popup/styles/main.css is 396px wide and the background opens an
approval window at 396x600. It is now 396x600, defined once near the top
of the file, and the hostile token symbol's frame takes its size from it.

assertAddressesFit() now measures the page at that size, then puts back
the size it found. Every page it measured, the popup's own screens and the
two approval prompts, was 1280x720, where a page never scrolls sideways,
so its sideways-scroll check could not fail. README's list of what the
Chrome suite leaves out says what sizing the page does not cover.

Comments in src/popup/index.html and tests/dustThreshold.test.js that
said 360x600 now say 396x600.

Model: opus-5-5

README.md

@@ -502,9 +502,10 @@ papered over:
   opens while libsodium is still loading, is not driven.
 - Approval windows open at 1280x720 whatever size the extension asks for. The
   site-connection prompt and the transaction approval are checked for sideways
-  scrolling at 396x600 by sizing the page itself, which leaves out the window's
-  frame and the page widening its window, so whether an approval screen fits its
-  window is checked in the Firefox suite only.
+  scrolling at 396x600 by sizing the page itself for that measurement only, and
+  the rest of each test runs at 1280x720. That leaves out the window's frame and
+  the page widening its window, so whether an approval screen fits its window is
+  checked in the Firefox suite only.
 
 Any test that drives a failure path on purpose declares the `console.error` it
 is about to provoke, via `errors.expect()`. That is not a mute: the declaration

tests/e2e/run.js

@@ -5035,10 +5035,17 @@ function addressRowReport(page) {
 // Measured at the popup's 396x600 (POPUP_VIEWPORT). Every page in this
 // context, approval windows included, is otherwise 1280x720 whatever size
 // the extension asks for, and a page that wide never scrolls sideways. The
-// page keeps the new size afterwards.
+// page is then put back to the size it had, so the size a later step runs at
+// does not depend on whether this one ran.
 async function assertAddressesFit(page, where) {
+    const sizeBefore = page.viewportSize();
     await page.setViewportSize(POPUP_VIEWPORT);
-    const report = await addressRowReport(page);
+    let report;
+    try {
+        report = await addressRowReport(page);
+    } finally {
+        await page.setViewportSize(sizeBefore);
+    }
     assert(
         report.rows.length > 0,
         where + ": no address rows were rendered, so nothing was measured",