feat(l1): admin L1 category settings page + route + settings card

New owner-gated pages/account/L1CategoriesPage.tsx: checkbox list of available
categories toggling enabled via l1Api.getCategories/setCategories, plus a read-only
'always excluded (safety)' hard-floor list. Registered lazy route /account/l1-categories
(ProtectedRoute requiredRole=owner) and an 'L1 AI build categories' card in the
AccountSettingsPage owner section. tsc -b + eslint clean.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/pages/AccountSettingsPage.tsx

@@ -18,6 +18,7 @@ import {
   RefreshCw,
   Server,
   Shield,
+  Wand2,
   UserCog,
   X,
 } from 'lucide-react'
@@ -662,6 +663,12 @@ export function AccountSettingsPage() {
                 title="Team categories"
                 description="Shared flow categories for your workspace"
               />
+              <SettingsRow
+                to="/account/l1-categories"
+                icon={<Wand2 className="h-4 w-4" />}
+                title="L1 AI build categories"
+                description="Which problem types the L1 assistant may build trees for"
+              />
               <SettingsRow
                 to="/account/target-lists"
                 icon={<Server className="h-4 w-4" />}