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-container-status.test.ts b/webui/src/web-components/sketch-container-status.test.ts
index ca1a8f5..7d01ac7 100644
--- a/webui/src/web-components/sketch-container-status.test.ts
+++ b/webui/src/web-components/sketch-container-status.test.ts
@@ -27,6 +27,8 @@
   ssh_available: false,
   in_container: true,
   first_message_index: 0,
+  diff_lines_added: 15,
+  diff_lines_removed: 3,
 };
 
 test("render props", async ({ mount }) => {