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/nextgraph-current-state.md

@@ -264,9 +264,8 @@ document is both (previous section), the shim uses an **indirection**:
 named doc-shim through its barrier (`ensureRepoOpen`) → read the account
 AUTHORITATIVELY. First login (no pointer): `doc_create` the doc-shim, publish the
 pointer, done. A **pointer fork** (two devices each writing a pointer before either
-synced) is **benign**: reconcile to the lexicographically-smallest doc-shim NURI
-(content-addressed, so every device converges), and no account data is lost — a
-non-canonical doc-shim's records are migrated forward on the next resolve.
+synced) is reconciled to the lexicographically-smallest doc-shim NURI
+(content-addressed, so every device converges on the same doc-shim).
 
 **The account-level retry is GONE.** Before this indirection the shim lived directly
 in the store-root graph, so an account read had no barrier and a cold 0 was ambiguous;
@@ -279,12 +278,12 @@ re-read of the **pointer** itself (`pointerGuard`, one write-once triple): it ca
 NEVER re-provision or fork an account — at worst it takes a couple extra reads to see
 a pointer that is still landing.
 
-**Migration (no existing account lost).** A wallet whose accounts were written under
-the OLD scheme has its `AccountRecord`s in the store-root graph, not a doc-shim. On
-resolution, `migrateLegacyRecords` reads that old location best-effort and RE-INSERTS
-each legacy record into the doc-shim (copy, not move — the store-root copy is left
-inert), BEFORE any "account absent" conclusion. So a legacy account is READ (and made
-barrier-authoritative going forward), never re-provisioned into a fork.
+**No legacy migration.** A wallet written under the OLD scheme (accounts directly in
+the store-root graph, no pointer) is NOT recovered: opening it under the current scheme
+simply provisions a fresh doc-shim, and the pre-indirection store-root records are
+ignored. This is deliberate — the only such wallets are dev data — so the resolution
+path carries no legacy-migration step; it always reads the account authoritatively from
+the doc-shim.
 
 ### The union is read-only — writes must target one document