fix: Don't crash if foreign key constraint is invalid in transaction (#1004)

ForeignKey constraints can be invalidated in the middle of a transaction
even if a later statement in the same transaction will make them valid
again. This seems to be causing production crashes.

Defer foreign key constraint checks until the end of the transaction to
prevent this.

core/database/src/main/kotlin/app/pachli/core/database/model/TimelineStatusEntity.kt

@@ -55,6 +55,7 @@ import java.util.Date
                 entity = TimelineAccountEntity::class,
                 parentColumns = ["serverId", "timelineUserId"],
                 childColumns = ["authorServerId", "timelineUserId"],
+                deferred = true,
             ),
         ]
         ),