fix(installer): replace confirmation prompt with 5-second countdown

curl | bash pipes stdin so read gets EOF and returns non-zero, which
set -euo pipefail treats as an error and aborts immediately. Replaced
the interactive prompt with a sleep 5 countdown — works whether the
script is piped or run directly.

Bumps version to 0.6.3.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "nixpanel-server",
-  "version": "0.6.2",
+  "version": "0.6.3",
   "private": true,
   "workspaces": [
     "server",