Make koffi optional dependency for cross-platform support (#1603)

Koffi is only used on Windows for VT input support and fails to build
on Termux/Android and Linux systems without build tools. Moving it to
optionalDependencies allows installation to succeed on all platforms
while maintaining Windows functionality.

package.json

@@ -45,8 +45,7 @@
 	"dependencies": {
 		"@mariozechner/jiti": "^2.6.5",
 		"@mariozechner/pi-coding-agent": "^0.30.2",
-		"get-east-asian-width": "^1.4.0",
-		"koffi": "^2.15.1"
+		"get-east-asian-width": "^1.4.0"
 	},
 	"overrides": {
 		"rimraf": "6.1.2",