Stop phantom-notification hangs and drop noisy "0초" progress label

Agents ended turns with "I'll wait … I'll be notified" expecting a
background-completion callback that this environment never delivers, so
the turn hung and left the planning sentence stuck in the channel. Add a
claude-platform rule that no such notification exists — finish within the
turn (foreground/poll) or ask the user for a follow-up.

Also suppress the elapsed-time suffix on progress messages until at least
one 5s bucket has elapsed, so freshly-created progress no longer shows a
meaningless "0초". Update the affected message-runtime expectations.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/message-turn-controller.ts

@@ -496,7 +496,10 @@ export class MessageTurnController {
         ? 0
         : Math.floor((Date.now() - this.progressStartedAt) / 5_000) * 5000;
 
-    const suffix = `\n\n${formatElapsedKorean(elapsedMs)}`;
+    // Skip the elapsed-time label until at least one 5s bucket has elapsed, so
+    // a freshly-created progress message doesn't show a meaningless "0초".
+    const suffix =
+      elapsedMs >= 5000 ? `\n\n${formatElapsedKorean(elapsedMs)}` : '';
     const body = this.composeProgressBody(text);
 
     this.persistProgressBody(body);