docs: comprehensive documentation updates and modernization

- Update BUILDING.md with current build system information
- Modernize various README files across the project
- Update CHANGELOG.md with recent changes
- Improve documentation consistency and formatting
- Update platform-specific documentation (iOS, Electron, Docker)
- Enhance test documentation and build guides

doc/migration-security-checklist.md

@@ -352,4 +352,4 @@ This security audit checklist ensures that the database migration maintains the
 
 **Reviewed By**: _______________
 
-**Approved By**: _______________ 
+**Approved By**: _______________