Add multi_value technical fields and FA category AI forms.

Support duplicatable free-text lists, always append سایر ویژگی‌ها on AI category forms, and fill leftover product specs into that field.

Co-authored-by: Cursor <cursoragent@cursor.com>

database/migrations/095_technical_field_type_multi_value.sql

@@ -0,0 +1,6 @@
+-- Free-text list field type for category technical forms (duplicatable values).
+DO $$ BEGIN
+  ALTER TYPE technical_field_type ADD VALUE 'multi_value';
+EXCEPTION
+  WHEN duplicate_object THEN NULL;
+END $$;