feat: race-free on-wake messages and explicit restart CLI

Decouple container restart from config updates — config CLI ops now only
write to the DB; restart is a separate `ncl groups restart` command with
--rebuild and --message flags. Add on_wake column to messages_in so wake
messages are only picked up by a fresh container's first poll, preventing
dying containers from stealing them during the SIGTERM grace window.
killContainer accepts an onExit callback for race-free respawn. Agent-
called restart auto-scopes to the calling session.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/container-runner.ts

@@ -190,10 +190,14 @@ async function spawnContainer(session: Session): Promise<void> {
 }
 
 /** Kill a container for a session. */
-export function killContainer(sessionId: string, reason: string): void {
+export function killContainer(sessionId: string, reason: string, onExit?: () => void): void {
   const entry = activeContainers.get(sessionId);
   if (!entry) return;
 
+  if (onExit) {
+    entry.process.once('close', onExit);
+  }
+
   log.info('Killing container', { sessionId, reason, containerName: entry.containerName });
   try {
     stopContainer(entry.containerName);