Widen settings.description to TEXT; run seeders in CI

The dualpath_single_machine setting description is 257 chars but
settings.description was varchar(255). On strict MySQL 8 an over-length
insert is a hard error 1406 (Data too long), so `flask seed settings`
failed on a fresh install; older/relaxed MySQL truncated silently and
hid it. Widen the column to TEXT (matches value, already TEXT) via core
migration 7d26.

CI only ran `flask db upgrade` + plugin install, never the seeders, so it
missed this. Add a seed step to the migrations-mysql job so a seeded row
that violates a column constraint fails CI on strict MySQL 8 instead of
shipping.

shopdb/core/models/setting.py

@@ -26,7 +26,7 @@ class Setting(db.Model):
     value = db.Column(db.Text, nullable=True)
     valuetype = db.Column(db.String(20), default='string')  # string, boolean, integer, json
     category = db.Column(db.String(50), default='general')  # For grouping in UI
-    description = db.Column(db.String(255), nullable=True)
+    description = db.Column(db.Text, nullable=True)
     createddate = db.Column(db.DateTime, default=_utcnow)
     modifieddate = db.Column(db.DateTime, default=_utcnow, onupdate=_utcnow)