feat:system: Add system utility library with executable check

Introduce a new `system-lib.el` module providing low-level system
utility functions, including function `cj/executable-exists-p` to
check for the availability of programs in PATH. Integrate this
library in `init.el`.

test(system): Add unit tests for executable check function

Create comprehensive unit tests for `cj/executable-exists-p` in
`system-lib.el`, ensuring coverage of normal, boundary and error
scenarios.

1 files changed, 1 insertions, 0 deletions

diff --git a/init.el b/init.el
index cc5df3ce..17d5e315 100644
--- a/init.el
+++ b/init.el
@@ -18,6 +18,7 @@
 
 ;; ---------------------------- System Configuration ---------------------------
 
+(require 'system-lib)            ;; low-level system utility functions
 (require 'config-utilities)      ;; enable for extra Emacs config debug helpers
 (require 'user-constants)        ;; paths for files referenced in this config
 (require 'host-environment)      ;; convenience functions re: host environment