The bundled CLI used to outrank PATH and known install locations, so
updating the desktop app silently switched people off their own OpenCode.
It is now the last resort: explicit env/settings, PATH, known install
locations, and shell discovery all win; the bundle only serves machines
with no OpenCode install at all. The env-runtime accepts an injectable
homedir so the fallback test stays hermetic on machines with a real
~/.opencode install.