Fix issue-write repo owner mapping and clear stale UI state on reset

- issue-write: derive owner/name from full_name since search_repositories
  minimal output omits the owner object (mirrors pr-write)
- pr-write/issue-write: clear available branch/label/assignee/milestone/type
  lists and filters in the toolInput reset effect so prefill effects can't
  match against the previous repo's stale data

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: mattdholloway

ui/src/apps/issue-write/App.tsx

@@ -432,6 +432,15 @@ function CreateIssueApp() {
     setSelectedIssueType(null);
     setSuccessIssue(null);
     setError(null);
+    // Clear available metadata (and filters) so prefill effects, which are gated
+    // on these lists being non-empty, can't match against the previous repo's data
+    // before the new repo's ui_get calls resolve.
+    setAvailableLabels([]);
+    setAvailableAssignees([]);
+    setAvailableMilestones([]);
+    setAvailableIssueTypes([]);
+    setLabelsFilter("");
+    setAssigneesFilter("");
     if (toolInput?.owner && toolInput?.repo) {
       setSelectedRepo({
         id: `${toolInput.owner}/${toolInput.repo}`,

ui/src/apps/pr-write/App.tsx

@@ -181,6 +181,12 @@ function CreatePRApp() {
     setSuccessPR(null);
     setError(null);
     setSubmittedTitle("");
+    // Clear branch list and filters so a new invocation doesn't briefly show stale
+    // branches from the previous repo (or allow selecting invalid options) before the
+    // new repo's ui_get branches call resolves.
+    setAvailableBranches([]);
+    setBaseFilter("");
+    setHeadFilter("");
     if (toolInput?.owner && toolInput?.repo) {
       setSelectedRepo({
         id: `${toolInput.owner}/${toolInput.repo}`,