plum

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

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

refactor(libs/std): rename files to match their primary class name

feat(plum): make Str a real class instead of a special-cased primitive

improvements