docs: update mining demo and scale video crops

- Refresh mining demo assets and documentation references
- Scale mpv crop coordinates for resized OBS recordings

docs-site/demos.md

@@ -5,7 +5,7 @@ Short recordings of SubMiner's key features and integrations from real playback
 <script setup>
 import { withBase } from 'vitepress';
 
-const v = '20260301-1';
+const v = '20260819-1';
 </script>
 
 ## Anki Card Mining & Enrichment

docs-site/index.md

@@ -88,7 +88,7 @@ features:
 <script setup>
 import { withBase } from 'vitepress';
 
-const demoAssetVersion = '20260223-2';
+const demoAssetVersion = '20260819-1';
 </script>
 
 <div class="landing-shell">