Phase 5a: add configurable Jai module roots

CHANGELOG.md

@@ -21,8 +21,10 @@
 - Go-to-definition references for `#import` and `#load`, including project-relative
   files and the local Jai module layout (`Name.jai` or `Name/module.jai`).
 - Basic completion for Jai keywords, compiler directives, and module/file paths.
+- Project-level Jai module/import root settings with ordered custom roots.
 - Go-to-definition for procedure and type symbols in the same file and through
-  loaded or imported Jai files.
+  loaded, imported, or configured external Jai files.
+- Indexed external Jai roots so find-usages can cross project/library boundaries.
 - Rename and find-usages support for declaration names and resolved references.
 
 ### Known gaps
@@ -31,8 +33,5 @@
   not have inner PSI.
 - `#asm` bodies remain intentionally opaque; assembly instructions do not have
   inner PSI or structure entries.
-- Import resolution currently uses fixed project/module roots and the local Jai
-  installation; configurable module roots and custom compiler `-import_dir`
-  arguments are planned.
 - Module-qualified members, procedure parameters, and struct fields do not yet
   have symbol resolution.