인증 요청 안정화와 월간 메일 한도 적용

api/src/db.js

@@ -78,6 +78,20 @@ export function initDb(dbPath) {
 
         CREATE INDEX IF NOT EXISTS idx_auth_tokens_user_type
         ON auth_tokens(user_id, type);
+
+        CREATE TABLE IF NOT EXISTS email_send_logs (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            user_id INTEGER NOT NULL,
+            type TEXT NOT NULL,
+            month_key TEXT NOT NULL,
+            status TEXT NOT NULL DEFAULT 'reserved',
+            created_at TEXT NOT NULL DEFAULT (datetime('now')),
+            sent_at TEXT,
+            FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
+        );
+
+        CREATE INDEX IF NOT EXISTS idx_email_send_logs_user_month
+        ON email_send_logs(user_id, month_key, status);
     `);
 
     const deckCols = db.prepare('PRAGMA table_info(decks)').all();