test(auth): add regression coverage proving v2 register reaches the fixed handler

[datvt243]

Summary

Closes #156. The originally buggy file (src/api/v1/auth/services/register.ts, missing await on bcryptGenerateSalt) no longer exists — it was removed by consolidate-v1-v2-auth (issue #77, SEALED 2026-08-29), which merged v1/v2 auth into one shared implementation. v2/auth.route.ts now wires /register to the same authRegister controller v1 uses, whose handlerRegister already awaits bcryptGenerateSalt correctly (already indirectly proven by the existing auth.service.test.ts assertion). The diagram node was never backfilled after the consolidation.

• src/__tests__/auth/v2AuthRoute.test.ts — asserts v2's /register route handler is the literal same authRegister function reference as v1 — proves v2 reaches the already-correct, already-tested handler, not a separate still-broken code path.
• agent-hub/: backfilled evidence (implementer + verifier) and sealed node fix-v2-register-missing-await.

Commits

• 5437632 test(auth): add regression coverage proving v2 register reaches the fixed handler
• (+ a merge commit syncing origin/staging, needed since this branch was cut before the other 4 issues in this batch merged)

Test plan

• npm test — 141 passed, 141 total on the original commit (independently re-run by the verifier subagent); 150 passed, 150 total after syncing staging
• npm run build — clean

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