fix(web): setup allows adding a printer with no controller configured

Second half of the printer/relay decoupling: the category section's
add-button gate ("add a controller first — a printer points at one of
its relays") blocked every non-access category while zero controllers
existed — hit on the lab bench (USB printer test, no relays on hand).
Printers don't bind (role + failoverRank route jobs), so the gate now
exempts them like the form's requirement already does.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

apps/web/src/SetupWizard.tsx

@@ -257,8 +257,10 @@ function CategorySection({
   const [formFor, setFormFor] = useState<Assignment | "new" | null>(null);
   const [warnings, setWarnings] = useState<string[]>([]);
 
-  // Binding categories need a controller to point at first.
-  const isBound = category !== "access";
+  // Binding categories need a controller to point at first. Printers do NOT bind
+  // (role + failoverRank route print jobs — see printer-routing.ts), so they are
+  // addable on a controller-less box (e.g. the lab bench testing a USB printer).
+  const isBound = category !== "access" && category !== "printer";
   const blockedNoController = isBound && controllers.length === 0;
   const editing = formFor && formFor !== "new" ? formFor : undefined;