Phase 5: add rename and find usages

CHANGELOG.md

@@ -20,6 +20,10 @@
 - Folding for blocks, nested comments, and multi-line here-strings.
 - 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.
+- Go-to-definition for procedure and type symbols in the same file and through
+  loaded or imported Jai files.
+- Rename and find-usages support for declaration names and resolved references.
 
 ### Known gaps
 
@@ -29,3 +33,5 @@
   inner PSI or structure entries.
 - Import resolution uses the project/module roots and the local Jai installation;
   custom compiler `-import_dir` arguments are not discovered yet.
+- Module-qualified members, procedure parameters, and struct fields do not yet
+  have symbol resolution.