add NUT Server to the catalog

- NUT Server (instantlinux/nut-upsd) runs the Network UPS Tools server for a UPS connected to the host by USB: the installation proposes the UPS the host detects, passes it to the container, generates the password of the upsmon user and starts with the host; clients such as PeaNUT connect on port 3493.
- A recipe can ask for the UPS of the host: without one, the installation stops and says so, and the advanced installation lets the node be typed by hand.
- The catalog lists 335 applications.
- Tests for the proposed UPS, a host without one and the recipe.

AppImage/components/lxc-terminal-modal.tsx

@@ -382,6 +382,19 @@ export function LxcTerminalModal({
                 
                 return
               }
+
+              // The host prompt came back: pct enter could not enter the
+              // container. Show why and close, so the session is never left
+              // on the host shell under the container's name.
+              const reason = afterPctEnter.split(/\r?\n/).slice(0, -1)
+                .map((line) => line.trim()).filter(Boolean).join("\r\n")
+              if (reason) term.writeln(`\x1b[31m${reason}\x1b[0m`)
+              term.writeln(`\r\n\x1b[33m${/Failed to exec/.test(reason)
+                ? t("lxcTerminal.errors.noShell")
+                : t("lxcTerminal.errors.enterFailed")}\x1b[0m`)
+              isInsideLxcRef.current = true
+              ws.close()
+              return
             }
           }
         } else {