Take Claude Desktop from the repository that now carries it

It was `panama app claude-desktop`: a source build, because nothing packaged it.
Upstream publishes an RPM repository now, so the exception shrinks to adding
that repository -- and the result upgrades with `dnf upgrade` along with
everything else instead of needing a slow rebuild every time a version ships.

That moves it out of setup/apps/ and into the third-party section of
install-packages, beside Bun, Claude Code and RustDesk. It also means it is part
of ./install for the first time. The reason it was kept out was the build: slow,
wants the network throughout, and fails on an upstream that moved, which is the
failure the interview exists to prevent. A dnf install is none of those, and the
default dock pins com.anthropic.Claude, so a fresh machine was shipping a pin
for something the install had never put there.

The repository is added with upstream's own setup script rather than a .repo
file written out here. A baseurl copied into this repository is a pin by another
name; the script is the part upstream keeps correct. Both halves are skipped
when already present, so a re-run costs nothing.

The desktop entry id does not change -- it is still com.anthropic.Claude -- so
the dock pin and the notification rules carry over untouched. The new package
drops the nodejs dependency, which is what used to hide the missing-npm bug the
launcher search contract guards; its comment said "depends" in the present
tense and now says what actually happened.

tests/setup/launcher-search-contract

@@ -106,8 +106,9 @@ grep -q 'command -v npm' "$stage" \
 # Checking for npm is not enough. Node comes from nvm, whose script only an
 # interactive shell sources -- and a stage is not one, so npm is absent unless
 # the stage goes and gets it. This machine hid that: a system npm existed only
-# because Claude Desktop depends on nodejs. Without this line, a fresh install
-# builds no extension and says so in one line nobody reads.
+# because the Claude Desktop of the day pulled in nodejs. It no longer does, so
+# nothing hides it any more. Without this line, a fresh install builds no
+# extension and says so in one line nobody reads.
 grep -q '/etc/profile.d/nvm.sh' "$stage" \
     || note 'the extension build never sources nvm, so npm is missing on any machine without a system node'