V19: Convert legacy SQL Server TEXT columns to nvarchar(max) so emoji and other non-CP1252 characters round-trip correctly. No-op on Postgres/SQLite.

Background

Earlier migrations declared columns with Ecto's :text type. On Postgres and SQLite this maps to UTF-8 TEXT and preserves any Unicode. On the Tds adapter, :text falls through the catch-all type mapping in ecto_sql's Ecto.Adapters.Tds.Connection and emits the literal SQL Server TEXT type — a legacy, collation-bound, non-Unicode type (deprecated since SQL Server 2005). On a CP1252 collation (the default on many installs), characters outside the codepage — emoji, CJK, most non-Latin scripts — are silently replaced with ? on write.

This migration alters every affected column to nvarchar(max) on SQL Server only. Rows already stored as ? remain lost; the migration unblocks future writes.

Notes

• ALTER COLUMN text -> nvarchar(max) converts rows in place but is not online — it takes a schema lock proportional to table size. Consumers with large cyclium_episode_logs tables should plan maintenance accordingly.
• Nullability is preserved (cyclium_workflow_definitions.steps is NOT NULL; everything else is nullable).
• None of the target columns are indexed today, and nvarchar(max) can't participate in a regular B-tree index anyway — same as text couldn't.