feat(plugins): core read-only scripts and user plugin system

Introduce plugin/<id> installs (zip, HTTPS git, example, fork),
jerapah-plugin.json manifests with jerapah semver ranges, isolated
plugin dirs under data/plugins, and app version 0.1.0. Core scripts
are non-editable; get-current-time moves to examples/plugins.

Co-authored-by: Nasyarobby Putra <nasyarobby@gmail.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "jerapah-flow",
-  "version": "1.0.0",
+  "version": "0.1.0",
   "private": true,
   "description": "Script/workflow runner with admin UI",
   "type": "module",