When oh-my-opencode is installed via npm global install and run as a
compiled binary, import.meta.url returns a virtual bun path ($bunfs)
instead of the actual filesystem path. This caused getCachedVersion()
to return null, resulting in 'unknown' version display.
Add fallback using process.execPath which correctly points to the actual
binary location, allowing us to walk up and find the package.json.
Fixes#1182
28a0dd06c7