Own printers, driverless only

The fourth panel this desktop handed to GNOME Settings, and the last one
worth owning.

Driverless only, deliberately. Adding a printer that describes its own
capabilities over IPP is supported; choosing a PPD or fetching a vendor
driver is not, and the page says so rather than pretending. That
restraint is the whole design: a wrong driver produces a printer that
accepts jobs, reports success, and prints nothing, which is the worst
failure this page could ship because it looks like it worked. A printer
old enough to need a PPD stays a job for the system printer tool.

Printers and the queue are separate cards because they answer separate
questions. Which printers exist is one; where a document went is the
other, and it is the one that actually brings someone here -- so the
queue is a single list across every printer.

Device URIs are validated by scheme before reaching CUPS, whose backends
run as root. file: and pipe: do not lead to a printer and are refused
here rather than further down.

This machine has no printer, so the page was built against a temporary
CUPS queue that was created, exercised through the service, and removed;
the service was confirmed to observe the removal rather than merely
perform it. Discovery and the driverless add path are verified by their
refusals rather than against hardware.

Claude-Session: https://claude.ai/code/session_01BRvzt4H8XXLPVH5MyYdk9L

config/dot/quickshell/services/ShellState.qml

@@ -92,7 +92,7 @@ Singleton {
     }
 
     function openSettings(page: string): void {
-        const allowed = ["home", "appearance", "displays", "connectivity", "home-phone", "desktop", "sound", "notifications", "screen-intelligence", "shortcuts", "mouse", "privacy", "region", "accounts", "accessibility", "power", "datetime", "applications", "storage", "users", "sharing", "services", "about"];
+        const allowed = ["home", "appearance", "displays", "connectivity", "home-phone", "desktop", "sound", "notifications", "screen-intelligence", "shortcuts", "mouse", "privacy", "region", "accounts", "accessibility", "power", "datetime", "applications", "storage", "users", "sharing", "printers", "services", "about"];
         root.settingsPage = allowed.indexOf(page) >= 0 ? page : "home";
         DesktopPreferences.set("lastPage", root.settingsPage);
         root.settingsOpen = true;