docs: add work log for 2026-06-15 and update DB deletion policy in README

scratch/check_codes.cjs

@@ -0,0 +1,24 @@
+const mysql = require('mysql2/promise');
+require('dotenv').config();
+
+async function checkCodes() {
+  const connection = await mysql.createConnection({
+    host: process.env.DB_HOST,
+    user: process.env.DB_USER,
+    password: process.env.DB_PASS,
+    database: process.env.DB_NAME,
+    port: parseInt(process.env.DB_PORT || '3306')
+  });
+
+  console.log('--- Asset Codes Sample ---');
+  const [rows] = await connection.query('SELECT id, asset_code, purchase_date FROM asset_core WHERE id LIKE "PC_20260615_%" LIMIT 10');
+  console.log(rows);
+  
+  console.log('\n--- Other Asset Codes Sample ---');
+  const [rows2] = await connection.query('SELECT id, asset_code, purchase_date FROM asset_core WHERE id NOT LIKE "PC_20260615_%" AND asset_code IS NOT NULL LIMIT 5');
+  console.log(rows2);
+
+  await connection.end();
+}
+
+checkCodes().catch(console.error);