feat(dashboard): text filter for Overview workplans chart

Add a search field next to the Workplans by Repository mode selector so
operators can narrow large lists by title, repo, domain, filename, or owner.

dashboard/src/components/workplan-search.js

@@ -0,0 +1,22 @@
+/**
+ * Case-insensitive substring match for Overview "Workplans by Repository".
+ * Matches title, repo, domain, filename, owner, and id.
+ *
+ * @param {object} workplan  Row from overview workplan_rows
+ * @param {string} query     Free-text filter
+ * @returns {boolean}
+ */
+export function workplanMatchesSearch(workplan, query) {
+  const q = String(query ?? "").trim().toLowerCase();
+  if (!q) return true;
+  if (!workplan || typeof workplan !== "object") return false;
+  const haystack = [
+    workplan.title,
+    workplan.repo_label,
+    workplan.domain,
+    workplan.workplan_filename,
+    workplan.owner,
+    workplan.id,
+  ].filter(Boolean).join("\n").toLowerCase();
+  return haystack.includes(q);
+}