plum

feat(lang): remove type/class entirely, enum is the only declaration form

rename folders

feat(number): add Number enum, migrate Int/Float methods, fix Float interpolation

refactor(stdlib): move libs/std to top-level plum-std, gate Int/Float/Str imports

feat(plum): make Bool an ordinary import-gated enum, no hardcoded prelude

feat(examples): convert dop_visitor to enum syntax, add OOP trait counterpart