fix🐛: stop hand-writing the soft-delete condition, and check the count

Two things in front of the unique-index work, both safe on their own.

getSysMenuByRoleName carried "deleted_at is null" in its where clause.
GORM adds that condition itself for a model with a DeletedAt field, so
it was a duplicate — and one phrased as a column being null, which stops
being true the moment the column stops being nullable. A schema that
moves to a non-null delete marker would have turned this query into one
that matches nothing, silently, for admin users only.

SysDictType.Insert dropped the error from its duplicate check: a query
that failed left the count at zero and the insert went ahead as though
the name were free.

The test pins what the removed clause was there for. Its counter-proof
is Unscoped rather than deleting the field — taking ModelTime off the
model fails to compile, which proves nothing.

app/admin/service/sys_menu.go

@@ -395,7 +395,11 @@ func (e *SysMenu) getByRoleName(roleName string) ([]models.SysMenu, error) {
 	data := make([]models.SysMenu, 0)
 
 	if roleName == "admin" {
-		err = e.Orm.Where(" menu_type in ('M','C') and deleted_at is null").
+		// The soft-delete condition is GORM's to add: it appends one for the
+		// model's DeletedAt field on every query. Writing it by hand duplicates
+		// that and hard-codes what "deleted" looks like — a column that stops
+		// being nullable turns this clause into one that matches nothing.
+		err = e.Orm.Where("menu_type in ('M','C')").
 			Order("sort").
 			Find(&data).
 			Error