feat(nesdoctor): put the line on the clipboard, and ask for the JSON properly

Two problems with how the run ended, both about presentation rather than data.

The summary line was set in the same dim grey as the paragraphs around it and
had to be found, then hand-selected out of a terminal. It is now a reverse-video
block under a "Copy this" rule, and it is copied to the clipboard automatically
via wl-copy, xclip, xsel, pbcopy or clip -- whichever the desktop has. Where
none is present we say so and mention the package, so it works by itself next
time. Selecting a long line out of a terminal was the last step before we learn
anything, so it should not be work.

And the JSON was described defensively -- "goes nowhere unless you send it" --
which reads as though we expect to be distrusted, and inviting the doubt is a
good way to create it. The file is genuinely the more valuable artefact: it
carries every check with its reason, the full latency series, and installed
titles with sizes and launch times. So it now says that, says what it is for,
and asks for it: read through it, send it along if nothing in there bothers
you, and the line is already plenty if not.

The consent model does not change -- no server exists, nothing is uploaded, and
Steam still needs an explicit yes asked last. What changes is that we stop
apologising for asking.

apps/nesdoctor/README.md

@@ -21,8 +21,16 @@ rather than a promise about our intentions: there is nothing to switch on later.
 
 The shareable line carries **no hostname, no IP, no username, no game titles and
 no file paths** — a size band rather than a size, and an hour histogram rather
-than timestamps. The long version does include titles and paths, and it stays in
-`nesdoctor.json` on your disk.
+than timestamps. It is put on your clipboard at the end so pasting it is one
+keystroke.
+
+The long version lands in `nesdoctor.json`: every check with its reason, the
+full latency series, and your installed titles with sizes and launch times if
+you said yes to Steam. **That file is considerably more useful to us than the
+line** — it is what lets us size a game library and see which requirement
+actually stops people — so do have a read through it and send it along if
+nothing in there bothers you. Plain JSON, entirely optional, and the one-line
+version is already plenty.
 
 Reading your Steam library needs an explicit yes, and the question is asked last,
 after you have seen what this program does.