fix(update): rewrite nupst update for v4 (download install script instead of git pull)

The update command was still using v3 logic (git pull, setup.sh) which
doesn't work for v4 binary distribution.

Now it simply:
1. Downloads install.sh from main branch
2. Runs it (handles download, stop, replace, restart automatically)

This is much simpler and matches how v4 is distributed. No more git,
no more setup.sh, just download the latest binary.

deno.json

@@ -1,6 +1,6 @@
 {
   "name": "@serve.zone/nupst",
-  "version": "4.0.6",
+  "version": "4.0.7",
   "exports": "./mod.ts",
   "tasks": {
     "dev": "deno run --allow-all mod.ts",