fix(restheadspec,resolvespec): stop casting SqlNull-wrapped and citext columns to TEXT in filters

reflect.Type.Kind() on spectypes.SqlNull[T] wrappers (SqlInt16/32/64,
SqlFloat64, SqlBool, SqlString, and embedders like SqlTimeStamp) always
reports reflect.Struct, never the wrapped T. ValidateAndAdjustFilterForColumnType
treated those as "complex" columns and forced CAST(col AS TEXT) on eq/gt/lt
filters, e.g. CAST(atdetail.rid_parent AS TEXT) = '90446096', which can't
use the index on rid_parent.

Add spectypes.UnwrapKind to see through SqlNull wrappers to the underlying
Kind, and use it in GetColumnTypeFromModel so numeric/string SqlNull columns
are recognized correctly and compared natively.

Also stop unconditionally casting to TEXT for LIKE/ILIKE and add
reflection.IsCitextColumn: citext columns are already case-insensitive, so
casting them to TEXT flips to case-sensitive matching and defeats a citext
index.

pkg/reflection/model_utils_test.go

@@ -3,6 +3,8 @@ package reflection
 import (
 	"reflect"
 	"testing"
+
+	"github.com/bitechdev/ResolveSpec/pkg/spectypes"
 )
 
 // Test models for GORM
@@ -1047,6 +1049,22 @@ func TestGetColumnTypeFromModel(t *testing.T) {
 	}
 }
 
+// SqlNull-wrapped columns (e.g. nullable bigint foreign keys) must report the
+// wrapped value's Kind, not reflect.Struct, so numeric eq/gt/lt filters don't
+// get an unnecessary CAST(... AS TEXT) that defeats the column's index.
+type SqlNullFKModel struct {
+	RidParent spectypes.SqlInt64 `bun:"rid_parent" json:"rid_parent"`
+}
+
+func TestGetColumnTypeFromModel_SqlNullWrapper(t *testing.T) {
+	model := SqlNullFKModel{RidParent: spectypes.NewSqlInt64(90446096)}
+
+	result := GetColumnTypeFromModel(model, "rid_parent")
+	if result != reflect.Int64 {
+		t.Errorf("GetColumnTypeFromModel(rid_parent) = %v, want %v (SqlInt64 must unwrap to its numeric Kind)", result, reflect.Int64)
+	}
+}
+
 // ============= Tests for relation functions =============
 
 // Models for relation testing