feat: shared loading state + cleanup loading state management (#5835)

* feat: implement shared loading bar component and polished loading states across the app

* feat: align loading states + ensureQueryData changes

* fix: lint + bugs

* fix: skeleton for manage servers page

* fix: merge conflict fix

apps/app-frontend/src/providers/setup/loading-state.ts

@@ -0,0 +1,17 @@
+import type { LoadingStateProvider } from '@modrinth/ui'
+import { createLoadingStateCore, provideLoadingState } from '@modrinth/ui'
+
+/**
+ * Source of truth for the desktop app's loading state.
+ *
+ * Owns the token-based ref-counter directly (no Pinia store). Consumers
+ * obtain the same reactive state via `injectLoadingState()` from `@modrinth/ui`.
+ *
+ * Returns the provider so the call site (App.vue) can also use it directly
+ * without a second injection round-trip.
+ */
+export function setupLoadingStateProvider(): LoadingStateProvider {
+	const provider = createLoadingStateCore({ barEnabled: false })
+	provideLoadingState(provider)
+	return provider
+}