feat(coding-agent): added auto-backgrounding for long bash jobs to avoid blocking

- Added bash.autoBackground.enabled and bash.autoBackground.thresholdMs settings with defaults for background job behavior.
- Added auto-backgrounding support for long foreground bash commands with managed job state and timeout threshold.
- Updated bash prompts, job-protocol messages, and tool activation checks to use async and auto-background support.
- Added background bash completion integration with AsyncJobManager and end-to-end tests for short/long auto-background scenarios.

packages/coding-agent/src/async/index.ts

@@ -1 +1,2 @@
 export * from "./job-manager";
+export * from "./support";

packages/coding-agent/src/async/support.ts

@@ -0,0 +1,5 @@
+import type { Settings } from "../config/settings";
+
+export function isBackgroundJobSupportEnabled(settings: Pick<Settings, "get">): boolean {
+	return settings.get("async.enabled") || settings.get("bash.autoBackground.enabled");
+}