The loader resolved a namespace against one hardcoded root (src/jolt, .clj
only). Now it searches an ordered list (ctx env :source-paths, stdlib first)
and tries .clj then .cljc. init adds roots from the :paths opt and JOLT_PATH.
This is the foundation for loading deps.edn libraries; verified loading medley
from an added root. No change to stdlib loading (3913 suite baseline held).
