V160: Widen phoenix_kit_settings.value from varchar(255) to text.
V03 created the column as :string, which Ecto renders as VARCHAR(255),
while PhoenixKit.Settings.Setting has always validated :value at
max: 1000. Any setting between 256 and 1000 characters therefore passed the
changeset and then died at the database with a raw Postgrex.Error — not a
changeset error a form could render, but a 500.
Nothing was obviously over the limit until settings started carrying lists: the sitemap's default exclude patterns serialize to ~450 characters, so saving them was a guaranteed crash. Widening the column fixes the whole class rather than that one key.
varchar(n) → text is a catalog-only change in PostgreSQL: no table
rewrite, no data validation pass, and the ACCESS EXCLUSIVE lock is held
only for the metadata update.