feat(portal-bff): audit log foundation per ADR-0013

Lays down the append-only audit log: schema, migration with role
grants, NestJS AuditWriter service. Typed event-family methods,
separate AUDIT_DATABASE_URL pool, retention job, and live-DB
integration tests are explicitly listed as "wired as features
land" in ADR-0013 §Confirmation.

Schema (apps/portal-bff/prisma/schema.prisma):

- multiSchema preview enabled; datasource declares public + audit
  schemas.
- AuditEvent model with: id (uuid), createdAt, eventType (free-form
  in v1, will formalise into a catalogue once we have N stable
  types), audience (workforce|customer enum), actorIdHash, traceId,
  subject, outcome (success|failure|denied enum), payload (jsonb).
- Indexes on createdAt, eventType, traceId — covering the obvious
  query shapes (date-range scan, by event family, by trace for
  log-audit correlation).

Migration (prisma/migrations/*_init_audit_schema/migration.sql):

- CREATE TABLE / enums via Prisma's standard output.
- Append-only contract re-applied explicitly: ALTER TABLE / TYPE
  OWNER TO audit_owner, then GRANT INSERT to audit_writer, SELECT
  to audit_reader, SELECT+DELETE to audit_archiver. SELECT is
  required for archiver because Postgres needs SELECT on every
  column referenced in DELETE's WHERE clause to evaluate "older
  than retention" — granted explicitly in this PR rather than
  silently failing later.
- USAGE on the enum types granted to all three roles so audit_
  writer's INSERT does not fail with "permission denied for type".
- No GRANT for UPDATE / TRUNCATE to anyone, including audit_owner
  at runtime — only fresh schema migrations amend the table.

Service (apps/portal-bff/src/audit/):

- AuditWriter.recordEvent(input) — single entry point. Wraps every
  INSERT in a transaction whose first statement is `SET LOCAL ROLE
  audit_writer`, so the role contract holds at runtime even from
  the otherwise-privileged BFF connection. SET LOCAL is reset on
  COMMIT/ROLLBACK so the pool's next consumer sees the original
  role.
- traceId auto-resolved from the active OTel span context.
- actorIdHash auto-resolved from CLS (key 'actorIdHash') with
  explicit input-side override; null when neither is set
  (placeholder until ADR-0009 / ADR-0010 guards populate CLS).
- Errors propagate (no catch-and-swallow), per ADR-0013's
  "blocking writes: no audit ⇒ no action".
- AuditModule exposes the writer; wired into AppModule so any
  future feature module can inject it.

Tests (apps/portal-bff/src/audit/audit.service.spec.ts, 8 cases):

- Locks the transaction to audit_writer before INSERTing.
- Passes input fields through.
- Records Prisma.JsonNull when no payload is provided.
- Reads actorIdHash from CLS when not passed.
- Prefers explicit actorIdHash over CLS-resolved.
- Stores actorIdHash = null when neither input nor CLS has one.
- Captures the active OTel trace id.
- Stores traceId = null when no span is active.
- Propagates the underlying error (no swallow).

End-to-end smoke against local-dev Postgres (manual, via psql):

- INSERT under audit_writer: ok.
- UPDATE under audit_writer: "permission denied for table events".
- DELETE under audit_writer: "permission denied for table events".
- DELETE under audit_archiver (after the SELECT grant fix): ok,
  row removed.

ADR-0013 §Confirmation rewritten as "wired in foundation PR" /
"wired as features land", with the latter listing the typed
event-family methods, AUDIT_DATABASE_URL split, startup self-test
probe, retention purge job, salt-shared cross-correlation test,
and live-DB role-contract integration tests.

apps/portal-bff/prisma/migrations/20260510011453_init_audit_schema/migration.sql

@@ -0,0 +1,67 @@
+-- CreateSchema
+CREATE SCHEMA IF NOT EXISTS "audit";
+
+-- CreateEnum
+CREATE TYPE "audit"."AuditAudience" AS ENUM ('workforce', 'customer');
+
+-- CreateEnum
+CREATE TYPE "audit"."AuditOutcome" AS ENUM ('success', 'failure', 'denied');
+
+-- CreateTable
+CREATE TABLE "audit"."events" (
+    "id" UUID NOT NULL,
+    "created_at" TIMESTAMPTZ(6) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "event_type" TEXT NOT NULL,
+    "audience" "audit"."AuditAudience" NOT NULL,
+    "actor_id_hash" TEXT,
+    "trace_id" TEXT,
+    "subject" TEXT,
+    "outcome" "audit"."AuditOutcome" NOT NULL,
+    "payload" JSONB,
+
+    CONSTRAINT "events_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE INDEX "events_created_at_idx" ON "audit"."events"("created_at");
+
+-- CreateIndex
+CREATE INDEX "events_event_type_idx" ON "audit"."events"("event_type");
+
+-- CreateIndex
+CREATE INDEX "events_trace_id_idx" ON "audit"."events"("trace_id");
+
+-- ============================================================
+-- Append-only contract per ADR-0013
+-- ============================================================
+-- The schema-level DEFAULT PRIVILEGES set in
+-- infra/local/init/postgres/01-init.sql only fire when audit_owner
+-- creates the object. This migration runs as a privileged migrator
+-- (the same login that owns the public schema), so the table is
+-- initially owned by that user and audit_writer/reader/archiver
+-- have no grants. Re-apply the owner transfer + grants explicitly
+-- so the runtime role contract holds.
+
+ALTER TABLE "audit"."events" OWNER TO audit_owner;
+ALTER TYPE "audit"."AuditAudience" OWNER TO audit_owner;
+ALTER TYPE "audit"."AuditOutcome" OWNER TO audit_owner;
+
+GRANT INSERT ON "audit"."events" TO audit_writer;
+GRANT SELECT ON "audit"."events" TO audit_reader;
+-- audit_archiver needs both DELETE *and* SELECT: per ADR-0013 it
+-- removes rows "older than retention", which means evaluating a
+-- WHERE clause on `created_at`. Postgres requires SELECT on every
+-- column referenced in DELETE's WHERE, even when the row count is
+-- the only thing returned. SELECT here does NOT widen the contract
+-- — UPDATE / TRUNCATE remain ungranted to every role.
+GRANT SELECT, DELETE ON "audit"."events" TO audit_archiver;
+
+-- USAGE on the enum types is needed by every role that touches the
+-- column. Without it, audit_writer's INSERT fails with "permission
+-- denied for type audit.AuditAudience".
+GRANT USAGE ON TYPE "audit"."AuditAudience" TO audit_writer, audit_reader, audit_archiver;
+GRANT USAGE ON TYPE "audit"."AuditOutcome" TO audit_writer, audit_reader, audit_archiver;
+
+-- No GRANT for UPDATE / TRUNCATE to anyone, including audit_owner
+-- at runtime — schema migrations alone amend the table going
+-- forward.

apps/portal-bff/prisma/migrations/migration_lock.toml

@@ -0,0 +1,3 @@
+# Please do not edit this file manually
+# It should be added in your version-control system (e.g., Git)
+provider = "postgresql"