[javascript] added contracts and agent database management

nodejs/database/agents.js

@@ -0,0 +1,16 @@
+import db from './db.js';
+
+const addAgentStatement = db.prepare(`INSERT INTO agents(data) VALUES (json(?));`);
+const getAgentStatement = db.prepare(`SELECT data FROM agents;`);
+
+export function addAgent(agent) {
+	return addAgentStatement.run(JSON.stringify(agent)).lastInsertRowid;
+}
+
+export function getAgent() {
+	const data = getAgentStatement.get();
+	if (data === undefined) {
+		return null;
+	}
+	return data.data;
+}