Extend the push pipeline to Android devices through the Silo push
relay's /v1/fcm/send endpoint. push_devices gains platform-conditional
FCM token columns (encrypted at rest with row AAD, hashed like APNs
tokens), the generic POST /notifications/push/devices endpoint the
Android client already calls registers FCM tokens, and fanout,
operational dispatch, retries, and terminal UNREGISTERED device
disabling all reuse the existing Apple machinery. Delivery is gated by
a new notifications.android_push_delivery_enabled setting, advertised
through the capability endpoint's android_push block, and testable via
POST /admin/notifications/push/fcm/test.
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
