feat(follow): add user follows with activity inbox digest

src/main/resources/application.yml

@@ -75,6 +75,13 @@ app:
   rewards:
     # Pile Points of every user, after the nightly sync (23:55) and the image repair (01:30).
     settle-cron: "0 30 2 * * *"
+  follow:
+    # The hand changes of a followed user are one batch after this quiet time.
+    digest-ms: 600000
+    quiet-minutes: 10
+  inbox:
+    purge-cron: "0 15 3 * * *"
+    keep-days: 90
   account-cleanup:
     # Log only, delete nothing. Auth's nightly cleanup drives this; see the Deployment README before flipping it.
     dry-run: ${APP_ACCOUNT_CLEANUP_DRY_RUN:true}