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.

src/db/article.js

@@ -10,6 +10,11 @@ export async function getBySku(googleAuthId, sku) {
     return store.article.getBySku(googleAuthId, sku);
 }
 
+export async function getHistoryBySku(googleAuthId, sku) {
+    const store = await getStore();
+    return store.article.getHistoryBySku(googleAuthId, sku);
+}
+
 export async function updateBySku(googleAuthId, sku, data) {
     const store = await getStore();
     return store.article.updateBySku(googleAuthId, sku, data);