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/approvalDisplayFloor.test.js

@@ -1,11 +1,11 @@
 // The floor of the approval screen's amount line.
 //
 // Amounts are truncated to four decimal places for scannability (README.md,
-// Display Consistency). With the token's true scale resolved, that truncation
-// can still take a real amount below the floor and print it as `0.0000`: one
-// base unit of an 18-decimal token, or a few hundred of an 8-decimal one. On
-// the one screen whose job is to state what is being authorized, a nonzero
-// transfer or allowance then reads as nothing.
+// Amounts). With the token's true scale resolved, that truncation can still
+// take a real amount below the floor and print it as `0.0000`: one base unit of
+// an 18-decimal token, or a few hundred of an 8-decimal one. On the one screen
+// whose job is to state what is being authorized, a nonzero transfer or
+// allowance then reads as nothing.
 //
 // The invariant asserted here is narrow: a nonzero amount never renders as
 // zero. The four-decimal rule itself is unchanged, and the string the