fix(background-agent): extend default no-progress stale timeout to 30 minutes

Give never-updated background tasks a longer default window and keep the default-threshold regression coverage aligned with that behavior.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/features/background-agent/task-poller.test.ts

@@ -117,13 +117,13 @@ describe("checkAndInterruptStaleTasks", () => {
   })
 
   it("should use DEFAULT_MESSAGE_STALENESS_TIMEOUT_MS when messageStalenessTimeoutMs is not configured", async () => {
-    //#given — task started 15 minutes ago, no config for messageStalenessTimeoutMs
+    //#given — task started 35 minutes ago, no config for messageStalenessTimeoutMs
     const task = createRunningTask({
-      startedAt: new Date(Date.now() - 15 * 60 * 1000),
+      startedAt: new Date(Date.now() - 35 * 60 * 1000),
       progress: undefined,
     })
 
-    //#when — default is 10 minutes (600_000ms)
+    //#when — default is 30 minutes (1_800_000ms)
     await checkAndInterruptStaleTasks({
       tasks: [task],
       client: mockClient as never,