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/template_handler.go

@@ -37,6 +37,7 @@ func NewTemplateHandler(a *bootstrap.App) *TemplateHandler {
 				a.Cache,
 			),
 			a.LLM,
+			a.RabbitMQ,
 			knowledgeSvc,
 			a.GenerationStreams,
 			a.Config.Generation,