chore(client): retirer la migration legacy + alléger les logs d'accès

- Migration des comptes legacy supprimée (migrateLegacyRecords + garde migratedInto
  + call-sites). Un wallet pré-fix (records store-root, pas de pointeur) provisionne
  simplement un doc-shim frais; contenu legacy ignoré (voulu, données = dev). La
  résolution barrière-autoritative + anti-fork (resolvePointer/ensureRepoOpen/
  canonicalDoc/ensureInFlight/pointerGuard) est inchangée.
- Logs d'accès SDK préfixés [polyfill] + NURI tronqué via shortNuri() (retire
  did:ng:o: et :v:…, garde 8 chars) → moins verbeux.
  Ex: [polyfill] [user1] READ vDlwbZio… (resolvePointer) → 1 triple-rows

Tests: bun test unit 126/0. Docs (nextgraph-current-state/simulation/migration-guide)
mis à jour (migration legacy retirée du modèle décrit).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/simulation.md

@@ -107,7 +107,8 @@ public/protected/private stores — on top of one shared wallet.
   through its barrier, and reads the account authoritatively — so a fresh reconnecting
   session never mistakes sync-lag for "account absent" (which would provision a FORK).
   Full rationale — including why the old account-level retry (`provisionRetry`) is
-  removed and how legacy store-root records are migrated forward — is in
+  removed (pre-indirection store-root records are NOT recovered; such wallets are dev
+  data and simply get a fresh doc-shim) — is in
   [`nextgraph-current-state.md`](./nextgraph-current-state.md) §§ *Findable vs
   subscribable* / *The pointer → doc-shim indirection*. This map is the
   account→document trust root, which is why every untrusted value that reaches its