feat: initial fluxer codebase import

fluxer_devops/cassandra/migrations/20251202000000_push_devices.cql

@@ -0,0 +1,10 @@
+CREATE TABLE IF NOT EXISTS fluxer.push_devices (
+    user_id bigint,
+    device_id text,
+    fcm_token text,
+    platform text,
+    device_name text,
+    created_at timestamp,
+    updated_at timestamp,
+    PRIMARY KEY (user_id, device_id)
+);