optimize firebase reads

README.md

@@ -1 +1,19 @@
-# wgenerator
+# wgenerator
+
+## Admin migration
+
+If `songUsage` needs to be rebuilt from all existing shows, log in with a user that has the `admin` role and run this in the browser console:
+
+```js
+await window.wgeneratorAdmin.rebuildSongUsage()
+```
+
+The migration:
+
+- resets `songUsage` for all users
+- scans all shows and all `shows/{id}/songs` entries
+- rebuilds the per-user counters based on show ownership
+
+It returns a summary object with processed user, show and show-song counts.
+
+This is intended as a manual one-off migration and is read-heavy by design.