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/DynamicForm.svelte

@@ -55,7 +55,7 @@
     {#if schema && schema.properties}
         {#each Object.entries(schema.properties) as [key, prop]}
             <div class="flex flex-col">
-                <label for={key} class="mb-1 font-semibold text-gray-700">{prop.title || key}</label>
+                <label for={key} class="mb-1 font-semibold text-text">{prop.title || key}</label>
                 {#if prop.type === 'string'}
                     <input
                         type="text"
@@ -82,7 +82,7 @@
                 {/if}
             </div>
         {/each}
-        <button type="submit" class="w-full bg-green-500 text-white p-2 rounded-md hover:bg-green-600">
+        <button type="submit" class="w-full bg-success text-white p-2 rounded-md hover:bg-success">
             Run Task
         </button>
     {/if}