feat: add wallet settlement audit flow

apps/api/migrations/0025_audit_logs.sql

@@ -0,0 +1,32 @@
+CREATE TABLE IF NOT EXISTS gateway_audit_logs (
+  id uuid PRIMARY KEY DEFAULT gen_random_uuid(),
+  category text NOT NULL DEFAULT 'system',
+  action text NOT NULL,
+  actor_gateway_user_id uuid REFERENCES gateway_users(id) ON DELETE SET NULL,
+  actor_user_id text,
+  actor_username text,
+  actor_source text,
+  actor_roles jsonb NOT NULL DEFAULT '[]'::jsonb,
+  target_type text NOT NULL,
+  target_id text NOT NULL,
+  target_gateway_user_id uuid REFERENCES gateway_users(id) ON DELETE SET NULL,
+  target_gateway_tenant_id uuid REFERENCES gateway_tenants(id) ON DELETE SET NULL,
+  request_ip text,
+  user_agent text,
+  before_state jsonb NOT NULL DEFAULT '{}'::jsonb,
+  after_state jsonb NOT NULL DEFAULT '{}'::jsonb,
+  metadata jsonb NOT NULL DEFAULT '{}'::jsonb,
+  created_at timestamptz NOT NULL DEFAULT now()
+);
+
+CREATE INDEX IF NOT EXISTS idx_gateway_audit_logs_category_created
+  ON gateway_audit_logs(category, created_at DESC);
+
+CREATE INDEX IF NOT EXISTS idx_gateway_audit_logs_action_created
+  ON gateway_audit_logs(action, created_at DESC);
+
+CREATE INDEX IF NOT EXISTS idx_gateway_audit_logs_target
+  ON gateway_audit_logs(target_type, target_id, created_at DESC);
+
+CREATE INDEX IF NOT EXISTS idx_gateway_audit_logs_actor
+  ON gateway_audit_logs(actor_gateway_user_id, created_at DESC);