fix(username): prevent release errors when recording sync failures

[NotThatKindOfDrLiz]

Username release preparation returned HTTP 500 in the real local Worker runtime when Fastly sync was unavailable. Recording the sync failure called D1’s batch method without its database receiver.

Call db.batch with the receiver intact and add a receiver-sensitive regression test. Username ownership and release semantics are unchanged; there is no visual change.

Validation: the regression failed before the fix; all 496 Worker tests and npm run typecheck pass afterward. The mobile local-stack integration will exercise the real D1 runtime against this commit.

Supports divinevideo/divine-mobile#7692 and divinevideo/divine-mobile#7691.

[divine-roborev]

roborev: Combined Review (ec9da72)

Verdict: No findings at or above high severity.

---

Reviewers: 2 done | Synthesis: opencode | Total: 1m50s

[dcadenas]

The receiver-preserving D1 batch call addresses the sync-failure recording error without changing username ownership or release semantics.
No actionable findings remained at ec9da72.

Checks

• The receiver regression failed with the old invocation and passed with the fix.
• npm run test:once: 496 tests passed; npm run typecheck passed.
• Admin UI npm test: 29 tests and test typechecking passed; npm run build passed.
• CI tests, Worker typechecking, admin tests/build, and the semantic-title validation step succeeded on this head. CLA and roborev checks also passed.

The local validation tool could not execute reusable workflows, the multi-command admin test, or watch mode directly.
The underlying test/build commands were covered separately, and the semantic check ran in CI.
Real local Worker HTTP/mobile integration and deployment were not exercised in this review; mobile integration remains separate from this focused receiver repair.