fix(jira): always return HTTP 200 from jira-test + strip trailing slash

- jira-test now returns {status: "ok"|"error", message: ...} with
  HTTP 200 so Cloudflare never intercepts the response
- jira_service strips trailing slash from URL before creating Jira
  client (avoids double-slash in REST paths)
- Frontend reads data.status field instead of HTTP status code

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/SettingsPage.tsx

@@ -1046,8 +1046,14 @@ function JiraConfigSection() {
   const testMut = useMutation({
     mutationFn: testJiraConnection,
     onSuccess: (data) => {
-      setTestResult({ connectedAs: data.connected_as, url: data.jira_url });
-      setTestError(null);
+      // Backend always returns HTTP 200; status field tells us if it worked
+      if (data.status === "ok") {
+        setTestResult({ connectedAs: data.connected_as ?? "", url: data.jira_url ?? "" });
+        setTestError(null);
+      } else {
+        setTestError((data as { message?: string }).message ?? "Connection failed");
+        setTestResult(null);
+      }
     },
     onError: (err: Error) => {
       setTestError(err.message || "Connection failed");