Bun bug oven-sh/bun#27802 causes process.env to be empty when running inside a Linux sandbox (Landlock/seccomp).
This breaks npm resolution because PATH is missing, crashing pi on startup with:
Failed to run npm root -g: Executable not found in $PATH: "npm"
Add getSandboxEnv() to read /proc/self/environ as a fallback on Linux when process.env has zero keys.
Pass this env to all spawn calls in package-manager.ts.
Also fix runCommandSync error handling: check result.error in addition to result.status, and include result.error?.message in the error text so spawn failures (e.g. ENOENT) produce useful diagnostics instead of "null".
Fixes#3806
cbe421f877