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/shared/amountDisplay.js

@@ -1,4 +1,4 @@
-// The 4-decimal amount rule from README.md's Display Consistency section, and
+// The 4-decimal amount rule from README.md's Amounts section, and
 // the one exception to it, in one place. Three call sites had grown their own
 // copy of the truncation — the history and balance lists
 // (`src/shared/transactions.js`), the approval screen's ERC-20 amount line

src/shared/browserApi.js

@@ -240,10 +240,9 @@ function onStorageChanged(listener) {
 /**
  * Run `fn` while holding the browser's lock called `name`
  * (`navigator.locks`), and settle as `fn` settles. Every page of the extension
- * and its background share these locks, except a page in a Firefox private
- * window (README, "Stored state and its version"), so while one of them holds
- * `name` another asking for it waits, in the order they asked. The lock is let
- * go when `fn` settles, whether it resolved or rejected.
+ * and its background share these locks, so while one of them holds `name`
+ * another asking for it waits, in the order they asked. The lock is let go when
+ * `fn` settles, whether it resolved or rejected.
  *
  * Every write of the stored record holds the lock named after its key,
  * "autistmask", from its read to its write: saveState() in
@@ -266,8 +265,8 @@ function withLock(name, fn) {
 
 // `storage.session`, the browser's session storage: what is kept there lasts
 // until the browser closes. It survives the background worker being stopped
-// and started again, which module-level variables do not (README, Background
-// scheduling). The background keeps the connections allowed without
+// and started again, which module-level variables do not (README, The
+// background worker). The background keeps the connections allowed without
 // "Remember" there; see src/background/index.js. Firefox has it from version
 // 115, the minimum manifest/firefox.json declares.
 //