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/git/BranchSelector.svelte

@@ -69,20 +69,20 @@
   </div>
 
   {#if model.branchError}
-  <div class="max-h-32 overflow-y-auto rounded-lg border border-red-300 bg-red-50 p-3 text-sm text-red-800" role="alert">
+  <div class="max-h-32 overflow-y-auto rounded-lg border border-destructive-ring bg-destructive-light p-3 text-sm text-destructive" role="alert">
     <div class="flex items-start gap-2">
-      <svg xmlns="http://www.w3.org/2000/svg" class="mt-0.5 h-4 w-4 flex-shrink-0 text-red-500" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><circle cx="12" cy="12" r="10"/><path stroke-linecap="round" stroke-linejoin="round" d="M15 9l-6 6m0-6l6 6"/></svg>
+      <svg xmlns="http://www.w3.org/2000/svg" class="mt-0.5 h-4 w-4 flex-shrink-0 text-destructive" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><circle cx="12" cy="12" r="10"/><path stroke-linecap="round" stroke-linejoin="round" d="M15 9l-6 6m0-6l6 6"/></svg>
       <div class="flex-1 min-w-0">
         <p class="truncate">{model.branchError.message}</p>
         {#if model.branchError.next_steps?.length}
-        <ul class="mt-1 list-disc pl-4 text-xs text-red-700">
+        <ul class="mt-1 list-disc pl-4 text-xs text-destructive">
           {#each model.branchError.next_steps as step}
           <li>{step}</li>
           {/each}
         </ul>
         {/if}
       </div>
-      <button type="button" onclick={() => model.branchError = null} class="flex-shrink-0 rounded p-0.5 hover:bg-red-100" aria-label="Закрыть">
+      <button type="button" onclick={() => model.branchError = null} class="flex-shrink-0 rounded p-0.5 hover:bg-destructive-light" aria-label="Закрыть">
         <svg xmlns="http://www.w3.org/2000/svg" class="h-3.5 w-3.5" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path stroke-linecap="round" stroke-linejoin="round" d="M6 18L18 6M6 6l12 12"/></svg>
       </button>
     </div>
@@ -90,7 +90,7 @@
   {/if}
 
   {#if model.showCreate}
-    <div class="flex items-end gap-2 bg-gray-50 p-3 rounded-lg border border-dashed border-gray-200">
+    <div class="flex items-end gap-2 bg-surface-muted p-3 rounded-lg border border-dashed border-border">
       <div class="flex-grow">
         <Input
           bind:value={model.newBranchName}
@@ -104,7 +104,7 @@
         onclick={() => model.handleCreate()}
         disabled={model.loading || !model.newBranchName}
         isLoading={model.loading}
-        class="bg-green-600 hover:bg-green-700"
+        class="bg-success hover:bg-success"
       >
         {$t.git.create}
       </Button>