Merge feature/ticket60-ticket-assistant-no-reply into develop (#60)

Rendre visible l'échec « aucune réponse » de l'assistant de ticket :
stream sans Final ou Final vide → ReplyChunk::Error terminal visible,
plus jamais de tour muet. Backend + frontend, tests verts.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/application/src/agent/structured.rs

@@ -383,9 +383,11 @@ fn drain_stream_to_final(
         match event {
             ReplyEvent::Final { content } => return Ok(TurnOutcome::Completed(content)),
             ReplyEvent::RateLimited { resets_at_ms } => last_rate_limit = Some(resets_at_ms),
-            // TextDelta / Announcement / ToolActivity / Heartbeat : non terminaux.
+            // TextDelta / Announcement / ToolActivity / Error / Heartbeat : non terminaux
+            // pour ce drain synchrone ; seul Final est une réponse réussie.
             ReplyEvent::TextDelta { .. }
             | ReplyEvent::Announcement { .. }
+            | ReplyEvent::Error { .. }
             | ReplyEvent::ToolActivity { .. }
             | ReplyEvent::Heartbeat => {}
         }