Diffs name their chain; history shows the ruleset's diff

The ruleset's diff names the chain each hunk is in on its @@ line, as
git names the function. A history entry shows what it did to the
ruleset (web page, hc history diff, GET /history/{id}/diff), rebuilt
from the current configuration by stepping back through the later
entries. A changed setting is listed by its own fields
(builtins.drop_invalid) instead of the whole object.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/web/static/assets/ui.js

@@ -200,7 +200,12 @@ export function diffView(text) {
     if (line.startsWith("+++") || line.startsWith("---")) cls = "file";
     else if (line.startsWith("+")) cls = "add";
     else if (line.startsWith("-")) cls = "del";
-    else if (line.startsWith("@@")) cls = "hunk";
+    else if (line.startsWith("@@")) {
+      // "@@ -a,b +c,d @@ chain forward": the chain the hunk is in.
+      const m = line.match(/^(@@ .*? @@)(?: (.+))?$/);
+      box.append(h("div", { class: "hunk" }, m ? [m[1], m[2] ? [" ", h("span", { class: "block" }, m[2])] : null] : line));
+      continue;
+    }
     box.append(h("div", { class: cls }, line || " "));
   }
   return box;