fix(gui-v2): rename unused _bp mock arg to _ (no-unused-vars gate)

The project's no-unused-vars only ignores all-underscore names (/^_+$/u);
`_bp` in the @vueuse/core useBreakpoints mock failed it. Latent since
Task 3 — masked because the whole-codebase `pnpm lint` stylish formatter
OOMs (RangeError on the legacy-code message volume) and emitted no
results. Scoped errors-only lint surfaced it. 21/21 specs still green.

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

apps/app/src/components-v2/layout/__tests__/AppSidebar.spec.ts

@@ -34,7 +34,7 @@ const mockIsMobileRef = ref(false)
 vi.mock('@vueuse/core', () => ({
   breakpointsTailwind: {},
   useBreakpoints: () => ({
-    smaller: (_bp: string) => mockIsMobileRef,
+    smaller: (_: string) => mockIsMobileRef,
   }),
 }))
 

apps/app/src/components-v2/layout/__tests__/SidebarHeader.spec.ts

@@ -28,7 +28,7 @@ const mockIsMobileRef = ref(false)
 vi.mock('@vueuse/core', () => ({
   breakpointsTailwind: {},
   useBreakpoints: () => ({
-    smaller: (_bp: string) => mockIsMobileRef,
+    smaller: (_: string) => mockIsMobileRef,
   }),
 }))