feat: move readingListTag from database to PDS preferences
Store readingListTag in the com.kipclip.preferences PDS record alongside
dateFormat instead of the Turso database. This syncs the preference across
devices and keeps the database for secrets (Instapaper credentials) only.
The reading list tag input now instant-applies on blur, consistent with
the date format picker. The Instapaper trigger in the bookmarks route
fetches preferences in parallel with settings to get the tag value.