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

tests/dustThreshold.test.js

@@ -74,7 +74,7 @@ describe("parsing the dust threshold", () => {
 });
 
 describe("the rejection message", () => {
-    // README, Language & Labeling: error messages are full sentences.
+    // README, Wording: error messages are full sentences.
     test("is a full sentence naming the constraint", () => {
         expect(DUST_THRESHOLD_MESSAGE).toMatch(/^[A-Z].*\.$/);
         expect(DUST_THRESHOLD_MESSAGE).toContain("whole number of gwei");
@@ -95,9 +95,9 @@ describe("the flash line the message is shown in", () => {
     // NOT and CANNOT assert that the message fits inside it: jest runs on
     // the node environment here, with no layout engine, so every rendered
     // height is zero. An earlier version of this block claimed to pin the
-    // No Layout Shift policy with this regex, and it passed at any message
-    // length, including one that wrapped to two lines and pushed the
-    // settings view down 12px.
+    // reserved space rule in README, Appearance, with this regex, and it
+    // passed at any message length, including one that wrapped to two lines
+    // and pushed the settings view down 12px.
     //
     // The line cuts a message too long for it with an ellipsis (see
     // showFlash() in src/popup/views/helpers.js). The assertions that