feat: brain inline PDF viewer — reuses PdfInlinePreview from trips

- PDF detail sheet now shows inline rendered PDF pages
- Click to expand inline, "Full view" for overlay viewer
- Uses pdfjs-dist canvas rendering (same as trips app)
- Falls back to screenshot if no original upload found

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend-v2/src/lib/pages/brain/AtelierBrainPage.svelte

@@ -2,6 +2,7 @@
   import { onMount } from 'svelte';
 
   import { onDestroy } from 'svelte';
+  import PdfInlinePreview from '$lib/components/trips/PdfInlinePreview.svelte';
 
   interface BrainItem {
     id: string;
@@ -462,10 +463,18 @@
         <a class="detail-screenshot" href={selectedItem.url} target="_blank" rel="noopener">
           <img src="/api/brain/storage/{selectedItem.id}/screenshot/screenshot.png" alt="" />
         </a>
-      {:else if selectedItem.type === 'pdf' && selectedItem.assets?.some(a => a.asset_type === 'screenshot')}
+      {:else if selectedItem.type === 'pdf'}
+        {@const pdfAsset = selectedItem.assets?.find(a => a.asset_type === 'original_upload')}
+        {#if pdfAsset}
+          <PdfInlinePreview
+            url="/api/brain/storage/{selectedItem.id}/original_upload/{pdfAsset.filename}"
+            name={selectedItem.title || pdfAsset.filename}
+          />
+        {:else if selectedItem.assets?.some(a => a.asset_type === 'screenshot')}
           <div class="detail-screenshot">
             <img src="/api/brain/storage/{selectedItem.id}/screenshot/screenshot.png" alt="" />
           </div>
+        {/if}
       {:else if selectedItem.type === 'image' && selectedItem.assets?.some(a => a.asset_type === 'original_upload')}
         {@const imgAsset = selectedItem.assets.find(a => a.asset_type === 'original_upload')}
         <div class="detail-screenshot">