fix: kill agent-spawned bash trees and dev servers on dashboard shutdown

TUI quit ('q'/Ctrl+C) bypassed signal handlers via process.exit(0), and
neither shutdown path closed the HTTP server, so server.close()'s
stopAllDevServers() listener never ran. In-flight agent bash commands
(spawned detached for their own pgroup) were also never aborted, so
their subprocess trees — including vitest workers — survived as orphans.

Route the TUI quit through SIGINT so the registered shutdown handler
runs, await stopAllDevServers() in both shutdown paths, and abort
in-flight bash on every active agent session at the start of the
runtime drain so killProcessTree reaches every grandchild.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/dashboard/src/index.ts

@@ -1,4 +1,5 @@
 export { createServer, loadTlsCredentialsFromEnv, type ServerOptions } from "./server.js";
+export { stopAllDevServers, destroyAllDevServerManagers, getActiveProcessManagers } from "./dev-server-routes.js";
 export {
   createRuntimeLogger,
   getRuntimeLogSink,