ADR-013 Phase 4: move hardcoded plugin top-level routes into plugin route files

Core-router surgery (the Phase 4 prerequisite for lean builds): index.js
hardcoded six plugin-owned full-screen routes (parts-kiosk, TV, printer-qr x2,
usb-labels, printedparts-labels), so pruning any of those plugins broke the SPA
build on an unresolvable import. The router now also collects a `toplevel`
named export from each plugin route file (alongside the existing default =
AppLayout children) and spreads it into the top-level routes. Each of the six
routes moved into its owning plugin's route file (printedparts, printers, usb,
slides); index.js keeps only the core print pages that span asset types
(machine-badge, asset-label, asset-label-batch).

index.js now references zero plugin view components. Verified: all six route
paths are present in the built bundle and the moved routes resolve exactly like
the unchanged core print routes. Build + vitest + naming green.

frontend/src/router/routes/slides.js

@@ -0,0 +1,9 @@
+
+export const toplevel = [
+  {
+    path: '/tv',
+    name: 'tv',
+    component: () => import('../../views/TVDashboard.vue'),
+    meta: { plugin: 'slides' }
+  }
+]