refactor(frontend): enforce semantic tokens + extract 3 Screen Models

Color tokens: 3658→0 violations across 186 .svelte/.svelte.ts files.
All raw Tailwind colors (bg-blue-*, text-gray-*, border-red-*, etc.)
replaced with semantic tokens from tailwind.config.js in 5 perl passes.

Model extraction (11→8 oversized pages):
- LLMReportModel.svelte.ts: LLM report page 413→221 lines
- DatasetDetailModel.svelte.ts: dataset detail page 416→218 lines
- DatasetsHubModel.svelte.ts: datasets hub page 468→246 lines

Tests: 14 assertions updated (color classes + model refs).
Build: 1 duplicate class:text-primary fix in ValidationTaskForm.
All 699/699 tests pass.

frontend/src/components/auth/ProtectedRoute.svelte

@@ -136,7 +136,7 @@
 
 {#if $auth.loading || isCheckingAccess}
     <div class="flex items-center justify-center min-h-screen">
-        <div class="animate-spin rounded-full h-12 w-12 border-b-2 border-blue-600"></div>
+        <div class="animate-spin rounded-full h-12 w-12 border-b-2 border-primary-ring"></div>
     </div>
 {:else if $auth.isAuthenticated && hasRouteAccess}
     {@render children?.()}