Add article history by SKU and SSE update signals for live clients.

Expose getHistoryBySku as GET /article/:sku/history, and document mutation-emitted company signals via GET /events.

docs/api/routes/article/delete.md

@@ -15,6 +15,10 @@ Auth like GET by SKU.
 |-------|----------|------|-------------|
 | `sku` | yes | string | Article SKU |
 
+## Signals
+
+On success, emits SSE signal: `articles` (see [`GET /events`](../events.md)).
+
 ## Response `204`
 
 Deleted