feat: add dedicated clear_plate permission + full-page group editor (#446)

Add a new `printers:clear_plate` permission so admins can grant
plate-clearing ability without full `printers:control` access.
Existing groups with `printers:control` automatically receive the
new permission on startup via migration.

Replace the cramped permission modal in Settings with a dedicated
full-page group editor (`/groups/new`, `/groups/:id/edit`) featuring
search filtering, select all/clear all, category-level toggles,
and a responsive 2-column permission grid. Remove dead GroupsPage
code that was never routed.

- Backend: new Permission enum, category, defaults, endpoint guard, migration
- Frontend: GroupEditPage, updated routes, removed modal from SettingsPage
- Tests: 10 backend + 10 frontend tests for new permission and editor
- Docs: updated wiki (auth, printer-control, API), website, changelog
- i18n: added group editor keys to all 6 locale files (en/de/ja/fr/pt-BR/it)

frontend/src/components/PrinterQueueWidget.tsx

@@ -70,7 +70,7 @@ export function PrinterQueueWidget({ printerId, printerState, plateCleared }: Pr
         ) : (
           <button
             onClick={() => clearPlateMutation.mutate()}
-            disabled={clearPlateMutation.isPending || !hasPermission('printers:control')}
+            disabled={clearPlateMutation.isPending || !hasPermission('printers:clear_plate')}
             className="w-full py-2 px-3 rounded-lg bg-bambu-green/20 border border-bambu-green/40 text-bambu-green hover:bg-bambu-green/30 transition-colors text-sm font-medium flex items-center justify-center gap-2 disabled:opacity-50"
           >
             {clearPlateMutation.isPending ? (