On a machine where rustup has no default toolchain, tauri-cli calls
`cargo metadata` without specifying one and panics in its metadata thread
with no useful error — just an abort. The file lives at the project root
(not src-tauri/) because tauri-cli invokes cargo from there; rustup walks
up from the CWD, so the root copy is the one that gets picked up.
Also notes this in FORK.md so a future forker knows what they would hit
and why the file must exist.
