fix(zshrc): only alias k when the omz k plugin loaded

Lean plugin prefs drop k; an unconditional k=k -h alias then
points at nothing useful. Gate on the function the plugin defines.

.zshrc

@@ -292,4 +292,7 @@ command -v zoxide &> /dev/null && eval "$(zoxide init zsh)"
 # Short jump alias; expands at use time after zoxide defines `z`.
 alias j="z"
 
-alias k="k -h"       # show human readable file sizes, in kb, mb etc
+# k plugin ships a `k` function; only alias when it actually loaded.
+if (( $+functions[k] )); then
+    alias k="k -h"   # human-readable sizes
+fi