feat: persist collapse/expand state across navigation via localStorage

Move collapsedParents from ephemeral useState into IssueViewState,
which is already serialised to localStorage under the scoped key.
Navigating away and back now restores the exact collapsed/expanded
state the user left the list in.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

ui/src/components/IssuesList.tsx

@@ -47,6 +47,7 @@ export type IssueViewState = {
   groupBy: "status" | "priority" | "assignee" | "none";
   viewMode: "list" | "board";
   collapsedGroups: string[];
+  collapsedParents: string[];
 };
 
 const defaultViewState: IssueViewState = {
@@ -60,6 +61,7 @@ const defaultViewState: IssueViewState = {
   groupBy: "none",
   viewMode: "list",
   collapsedGroups: [],
+  collapsedParents: [],
 };
 
 const quickFilterPresets = [
@@ -219,7 +221,6 @@ export function IssuesList({
     return getViewState(scopedKey);
   });
   const [assigneePickerIssueId, setAssigneePickerIssueId] = useState<string | null>(null);
-  const [collapsedParents, setCollapsedParents] = useState<Set<string>>(new Set());
   const [assigneeSearch, setAssigneeSearch] = useState("");
   const [issueSearch, setIssueSearch] = useState(initialSearch ?? "");
   const deferredIssueSearch = useDeferredValue(issueSearch);
@@ -680,14 +681,14 @@ export function IssuesList({
                 const renderIssueRow = (issue: Issue, depth: number) => {
                   const children = childMap.get(issue.id) ?? [];
                   const hasChildren = children.length > 0;
-                  const isExpanded = !collapsedParents.has(issue.id);
+                  const isExpanded = !viewState.collapsedParents.includes(issue.id);
                   const toggleCollapse = (e: { preventDefault: () => void; stopPropagation: () => void }) => {
                     e.preventDefault();
                     e.stopPropagation();
-                    setCollapsedParents((prev) => {
-                      const next = new Set(prev);
-                      if (next.has(issue.id)) next.delete(issue.id); else next.add(issue.id);
-                      return next;
+                    updateView({
+                      collapsedParents: isExpanded
+                        ? [...viewState.collapsedParents, issue.id]
+                        : viewState.collapsedParents.filter((id) => id !== issue.id),
                     });
                   };