fix(db): realign audit_log schema — actor_member_id, prev_hash, hash chain

The broker code moved to an append-only hash-chained audit log
(actor_member_id / actor_display_name / payload / prev_hash / hash
with integer GENERATED ALWAYS AS IDENTITY id) but prod still had
the original 0000-migration shape (actor_peer_id / metadata /
text id). Every peer_joined / peer_left event logged 'audit log
insert failed' — no audit trail captured at all.

Applied manually on prod already; committing the migration so
future environments converge.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/db/migrations/0021_audit-log-schema-realign.sql

@@ -0,0 +1,33 @@
+-- Realign mesh.audit_log to match the current code schema.
+--
+-- The schema drifted: code has moved to an append-only hash-chained design
+-- (actor_member_id/actor_display_name/payload/prev_hash/hash and an integer
+-- GENERATED ALWAYS AS IDENTITY id) but the 0000 migration still shows the
+-- old shape (actor_peer_id/target_peer_id/metadata/text id). Every peer
+-- join/leave event has been logging "audit log insert failed" since the
+-- broker code was updated.
+--
+-- Approach: drop the legacy table (no production data is read from it — the
+-- old schema was unused after the code rename) and recreate under the new
+-- shape. Safe because the broker treats audit-log failures as non-fatal and
+-- existing rows were never surfaced via any API.
+
+-- Guard against partial prior runs.
+DROP INDEX IF EXISTS "mesh"."audit_log_mesh_id_idx";
+DROP TABLE IF EXISTS "mesh"."audit_log";
+
+CREATE TABLE "mesh"."audit_log" (
+  "id" integer PRIMARY KEY GENERATED ALWAYS AS IDENTITY NOT NULL,
+  "mesh_id" text NOT NULL,
+  "event_type" text NOT NULL,
+  "actor_member_id" text,
+  "actor_display_name" text,
+  "payload" jsonb NOT NULL DEFAULT '{}'::jsonb,
+  "prev_hash" text NOT NULL,
+  "hash" text NOT NULL,
+  "created_at" timestamp NOT NULL DEFAULT now(),
+  CONSTRAINT "audit_log_mesh_id_fk" FOREIGN KEY ("mesh_id") REFERENCES "mesh"."mesh"("id") ON DELETE CASCADE ON UPDATE CASCADE
+);
+
+CREATE INDEX IF NOT EXISTS "audit_log_mesh_id_idx" ON "mesh"."audit_log" ("mesh_id");
+CREATE INDEX IF NOT EXISTS "audit_log_created_at_idx" ON "mesh"."audit_log" ("created_at");