provision: auto-detect repo root instead of assuming ~/osctrl

[alvarofraguas]

Summary

• Replaces the hardcoded SOURCE_PATH=~/osctrl default in deploy/provision.sh with script-relative path detection: SOURCE_PATH="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
• This resolves the provisioning failure when the osctrl repo is cloned to a non-root user's home directory (or anywhere other than ~/osctrl)
• The -s PATH / --source PATH flag override still works as before

Closes #825