loop: add diff stats from sketch-base to HEAD in /state endpoint

Add lines added/removed statistics computed from sketch-base to current HEAD,
displayed in webui Diff mode button for quick change overview.

Co-Authored-By: sketch <hello@sketch.dev>
Change-ID: s3f10ecf39df6b581k
diff --git a/webui/src/web-components/sketch-app-shell.ts b/webui/src/web-components/sketch-app-shell.ts
index 29e12ba..e2d27a2 100644
--- a/webui/src/web-components/sketch-app-shell.ts
+++ b/webui/src/web-components/sketch-app-shell.ts
@@ -531,6 +531,8 @@
     ssh_error: "",
     in_container: false,
     first_message_index: 0,
+    diff_lines_added: 0,
+    diff_lines_removed: 0,
   };
 
   // Mutation observer to detect when new messages are added
@@ -1238,7 +1240,10 @@
         <!-- Last Commit section moved to sketch-container-status -->
 
         <!-- Views section with tabs -->
-        <sketch-view-mode-select></sketch-view-mode-select>
+        <sketch-view-mode-select
+          .diffLinesAdded=${this.containerState?.diff_lines_added || 0}
+          .diffLinesRemoved=${this.containerState?.diff_lines_removed || 0}
+        ></sketch-view-mode-select>
 
         <div class="refresh-control">
           <button