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/bootstrap/bootstrap.go

@@ -94,7 +94,7 @@ func New(configPath string) (*App, error) {
 	vectorStore := retrieval.NewQdrantStore(cfg.Qdrant, logger)
 	objectStorageClient := objectstorage.New(cfg.ObjectStorage, logger)
 	auditLogs := auditlog.NewAsyncWriter(pool, logger)
-	generationStreams := stream.NewGenerationHub()
+	generationStreams := stream.NewGenerationHub(mqClient)
 	appCache := cache.New(cfg.Cache.Driver, rdb)
 
 	if cfg.Server.Mode == "release" {