feat(generation): migrate article generation and template-assist to RabbitMQ queues

Replace in-process generation with queue-based async execution via
RabbitMQ. Add generation task runtime for lifecycle management, article
generation payload/queue abstractions, and template-assist queue publisher.
Refactor prompt generation service to support batch generation with
per-item error tracking. Update stream hub to bridge queue events to SSE.

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

server/internal/tenant/transport/article_handler.go

@@ -51,6 +51,7 @@ func NewArticleHandler(a *bootstrap.App) *ArticleHandler {
 		promptGenerateSvc: app.NewPromptRuleGenerationService(
 			a.DB,
 			a.LLM,
+			a.RabbitMQ,
 			knowledgeSvc,
 			a.GenerationStreams,
 			a.Config.Generation,
@@ -369,6 +370,11 @@ func (h *ArticleHandler) Stream(c *gin.Context) {
 		return
 	}
 
+	fallback := buildGenerationSnapshot(detail)
+	if snapshot, ok := h.streams.Snapshot(id); !ok || (fallback.Done && snapshot.Status != fallback.Status) {
+		h.streams.Seed(fallback)
+	}
+
 	events, snapshot, cancel := h.streams.Subscribe(id)
 	defer cancel()
 
@@ -377,20 +383,10 @@ func (h *ArticleHandler) Stream(c *gin.Context) {
 			return
 		}
 		flusher.Flush()
+		if snapshot.Done {
+			return
+		}
 	} else {
-		fallback := stream.GenerationEvent{
-			Type:      "snapshot",
-			ArticleID: detail.ID,
-			Status:    detail.GenerateStatus,
-			Done:      detail.GenerateStatus == "completed" || detail.GenerateStatus == "failed",
-			UpdatedAt: time.Now().UTC(),
-		}
-		if detail.Title != nil {
-			fallback.Title = *detail.Title
-		}
-		if detail.MarkdownContent != nil {
-			fallback.Content = *detail.MarkdownContent
-		}
 		if err := writeSSE(c, fallback.Type, fallback); err != nil {
 			return
 		}
@@ -455,6 +451,32 @@ func writeSSE(c *gin.Context, event string, payload interface{}) error {
 	return nil
 }
 
+func buildGenerationSnapshot(detail *app.ArticleDetailResponse) stream.GenerationEvent {
+	event := stream.GenerationEvent{
+		Type:      "snapshot",
+		ArticleID: detail.ID,
+		Status:    detail.GenerateStatus,
+		Done:      detail.GenerateStatus == "completed" || detail.GenerateStatus == "failed",
+		UpdatedAt: time.Now().UTC(),
+	}
+	if detail.Title != nil {
+		event.Title = *detail.Title
+	}
+	if detail.MarkdownContent != nil {
+		event.Content = *detail.MarkdownContent
+	}
+	if detail.GenerateStatus == "completed" {
+		event.Type = "completed"
+	}
+	if detail.GenerateStatus == "failed" {
+		event.Type = "error"
+		if detail.GenerationErrorMessage != nil {
+			event.Error = *detail.GenerationErrorMessage
+		}
+	}
+	return event
+}
+
 func resolveOptimizeStreamErrorMessage(appErr *response.AppError) string {
 	if appErr == nil {
 		return "optimize selection failed"