feat(setup): headless-aware Claude sign-in pre-message

The pre-message printed by setup/register-claude-token.sh used to
say "A browser window will open for you to sign in with your
Claude account." Accurate on a laptop or desktop, but a lie on
headless devices (Pi, SSH'd-into Linux server, CI) where the
browser auto-open never lands and the user actually has to copy
the URL `claude setup-token` prints to another device.

Add a small bash isHeadless check (mirrors `isHeadless()` in
setup/platform.ts: Linux without DISPLAY / WAYLAND_DISPLAY) and
swap the heredoc accordingly:

  - Headless: "A sign-in link will appear for you to sign in with
    your Claude account. When you finish, we'll save the token
    to your OneCLI vault automatically."
  - GUI: existing "A browser window will open…" copy, unchanged.

The trailing "Press Enter to continue, or edit the command first."
line and the actual `claude setup-token` invocation are unchanged
— only the leading sentence flips.

setup/register-claude-token.sh

@@ -51,13 +51,34 @@ command -v script >/dev/null \
 tmpfile=$(mktemp -t claude-setup-token.XXXXXX)
 trap 'rm -f "$tmpfile"' EXIT
 
-cat <<'EOF'
+# Detect headless. Mirrors `isHeadless()` in setup/platform.ts: on Linux
+# with neither DISPLAY nor WAYLAND_DISPLAY set, no graphical session
+# exists, so `claude setup-token` won't be able to auto-open a browser
+# and the user will need to copy the printed sign-in URL by hand. The
+# pre-message copy below is swapped accordingly so we don't promise a
+# browser pop that will never happen.
+is_headless=0
+if [ "$(uname -s)" = "Linux" ] && [ -z "${DISPLAY:-}" ] && [ -z "${WAYLAND_DISPLAY:-}" ]; then
+  is_headless=1
+fi
+
+if [ "$is_headless" = "1" ]; then
+  cat <<'EOF'
+A sign-in link will appear for you to sign in with your Claude account.
+When you finish, we'll save the token to your OneCLI vault automatically.
+
+Press Enter to continue, or edit the command first.
+
+EOF
+else
+  cat <<'EOF'
 A browser window will open for you to sign in with your Claude account.
 When you finish, we'll save the token to your OneCLI vault automatically.
 
 Press Enter to continue, or edit the command first.
 
 EOF
+fi
 
 cmd="claude setup-token"
 if [ "${BASH_VERSINFO[0]:-0}" -ge 4 ]; then