refactor: session handler

prisma/schema/auth.prisma

@@ -53,6 +53,11 @@ model Certificate {
 }
 
 model Session {
-    token String @id
-    data  Json
+    token     String   @id
+    expiresAt DateTime
+
+    userId String
+    user   User?  @relation(fields: [userId], references: [id])
+
+    data Json // misc extra data
 }

prisma/schema/user.prisma

@@ -14,7 +14,8 @@ model User {
     collections   Collection[]
     articles      Article[]
 
-    tokens APIToken[]
+    tokens   APIToken[]
+    sessions Session[]
 }
 
 model Notification {