feat(core-audit): admin tRPC procedure for eraseSubject

Adds auditProcedure (adminOnly middleware + defineErrorMiddleware([])) in
core-audit/src/integrations/api/procedures.ts. Adds createAuditRouter that
captures an IAuditLog and exposes a single eraseSubject mutation with zod
input validation. Non-admins receive FORBIDDEN. Barrel re-exports
pseudonymize, createAuditErasureHook, createAuditRouter, auditRouter,
AuditRouter, auditProcedure, AdminTrpcUser. Adds AUDIT_PSEUDONYM_SALT to
turbo.json globalEnv to clear lint warnings.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

turbo.json

@@ -21,7 +21,8 @@
     "SENTRY_ENVIRONMENT",
     "VERCEL_GIT_COMMIT_SHA",
     "NEXT_PUBLIC_VERCEL_GIT_COMMIT_SHA",
-    "VERCEL_ENV"
+    "VERCEL_ENV",
+    "AUDIT_PSEUDONYM_SALT"
   ],
   "boundaries": {
     "tags": {