fix: remove unintentional deleted_at filter from getThreadCheckpointContextThreadRow

The new targeted query added AND threads.deleted_at IS NULL, but the
original code path returned all threads regardless of deletion status.
This caused checkpoint diff requests for soft-deleted threads to fail
with a CheckpointInvariantError instead of returning diff data.

Author: cursoragent

apps/server/src/orchestration/Layers/ProjectionSnapshotQuery.ts

@@ -407,7 +407,6 @@ const makeProjectionSnapshotQuery = Effect.gen(function* () {
         INNER JOIN projection_projects AS projects
           ON projects.project_id = threads.project_id
         WHERE threads.thread_id = ${threadId}
-          AND threads.deleted_at IS NULL
         LIMIT 1
       `,
   });