A community based topic aggregation platform built on atproto

test(integration): migrate batch 1 (29 files) to testkit.DB per-test clones master

Phase 3 task 7. aggregator_e2e through concurrent_scenarios: 115 setup sites (103 setupTestDB calls + 12 hand-rolled sql.Open/goose blocks) become testkit.DB(t) clones; 19 unscoped DELETE FROM statements and one per-file cleanup fn deleted rather than ported; two tests turned out to need no database at all. Isolation verified by running a previously PK-colliding pair concurrently. make ci green 3399/0 at 142s. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>