feat: extends database schema with sync and creation timestamps

internal/database/migrations/1_feed.sql

@@ -3,7 +3,8 @@ CREATE table feed (
   id INTEGER PRIMARY KEY,
   name text NOT NULL,
   url text NOT NULL UNIQUE,
-  addedAt DATETIME DEFAULT CURRENT_TIMESTAMP NOT NULL
+  createdAt DATETIME DEFAULT CURRENT_TIMESTAMP NOT NULL,
+  lastSyncedAt DATETIME DEFAULT CURRENT_TIMESTAMP NOT NULL
 );
 
 -- +migrate Down