docs: code comments name the headings README has now (closes #724)

The README rewrite renamed or merged several headings that comments still
cited. Each comment now names the current heading. Line number citations of
README become headings too, and one test name drops its line numbers.

The e2e workflow's citations of "In CI" are dropped, because no section has what
they pointed at. Its comment also corrects what it says about required jobs and
open reports.

The comment on withLock() no longer states a Firefox private window exception,
because the manifest keeps the extension out of those windows.

Two comments also take corrections from reviews: the cases with no total in
DeleteAddress's warning, and the screens that say a swap's amount could not be
decoded.

Model: opus-5-5

src/popup/views/settings.js

@@ -265,7 +265,7 @@ async function renderSiteLists() {
 // A network switch, made by the user here or saved by the background once the
 // user approved a site's request (src/popup/index.js), leaves every screen on
 // the page showing the previous network. Two functions leave the page as
-// README's Screen Map describes:
+// README's Navigation section describes:
 //
 // - cutViewStack(), before the switch is saved, so that save keeps the cut for
 //   a popup closed straight after