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/api/settings.ts

@@ -178,7 +178,12 @@ export async function updateJiraConfig(payload: JiraConfigUpdate): Promise<JiraC
   return data;
 }
 
-export async function testJiraConnection(): Promise<{ status: string; connected_as: string; jira_url: string }> {
+export async function testJiraConnection(): Promise<{
+  status: "ok" | "error";
+  connected_as?: string;
+  jira_url?: string;
+  message?: string;
+}> {
   const { data } = await client.post("/system/jira-test");
   return data;
 }