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>

container/agent-runner/src/poll-loop.ts

@@ -67,9 +67,11 @@ export async function runPollLoop(config: PollLoopConfig): Promise<void> {
   clearStaleProcessingAcks();
 
   let pollCount = 0;
+  let isFirstPoll = true;
   while (true) {
     // Skip system messages — they're responses for MCP tools (e.g., ask_user_question)
-    const messages = getPendingMessages().filter((m) => m.kind !== 'system');
+    const messages = getPendingMessages(isFirstPoll).filter((m) => m.kind !== 'system');
+    isFirstPoll = false;
     pollCount++;
 
     // Periodic heartbeat so we know the loop is alive