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 comment on withLock() drops its reference, because no README section states
its Firefox private window exception.

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.

Comments under tests/ are not changed.

Model: opus-5-5

script/lib/package.js

@@ -1,7 +1,7 @@
 // Turn a verified dist/ into the two distributable archives.
 //
 // Invoked by script/package, which runs `make build` first so that dist/ has
-// already been checked against the build's own receipt (see the Build Receipts
+// already been checked against the build's own receipt (see the Builds
 // section of README.md). This program does not build anything and does not
 // write into dist/: it reads the emitted tree and writes release/.
 //