feat: add task sorting & filtering

adds filtering by task status (completion date, incomplete, completion)
adds filtering by task metadata (task name, labels, members, due date)
adds sorting by task name, labels, members, and due date

internal/graph/schema/_models.gql

@@ -129,6 +129,7 @@ type Task {
   description: String
   dueDate: Time
   complete: Boolean!
+  completedAt: Time
   assigned: [Member!]!
   labels: [TaskLabel!]!
   checklists: [TaskChecklist!]!