Update WebNN architecture diagram (#908)

DirectML -> Windows ML
TensorFlow Lite Web -> LiteRT.js

SVG export produced with Mermaid Live Editor patched with:
perl -pi -e 's/ / /g' webnn_arch.svg

Author: anssiko

content/webnn_arch.svg

@@ -31,7 +31,7 @@ flowchart TD
   end
 
   subgraph Frameworks
-    Framework(ONNX Runtime Web, LiteRT)
+    Framework(ONNX Runtime Web / LiteRT.js)
   end
 
   subgraph Browser_APIs[Browser APIs]
@@ -41,7 +41,7 @@ flowchart TD
   end
 
   subgraph Native_ML_APIs[Native ML APIs]
-    MLAPI[DirectML / LiteRT / Core ML]
+    MLAPI[Windows ML / LiteRT / Core ML]
   end
 
   subgraph Hardware