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.

The e2e workflow's citations of "In CI" are dropped, because no section has what
they pointed at.

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

tests/manifest.test.js

@@ -165,9 +165,9 @@ describe("declared icons", () => {
     });
 });
 
+// README, Installing on Firefox: the extension does not run in private windows.
 // Firefox gives a page in a private window locks of its own, so that page's
-// save could land between the background's read and its write (README,
-// "Stored state and its version").
+// save could land between the background's read and its write.
 describe("private windows", () => {
     test("a page in a firefox private window cannot read or write extension storage", () => {
         expect(readManifest("firefox").incognito).toBe("not_allowed");