Naming the file tauri.windows.conf.json made Tauri merge it into every Windows
build automatically, and externalBin is resolved by the build script — so a
bare `cargo check` in src-tauri started failing with "resource path
binaries\ostp-tun-helper-x86_64-pc-windows-msvc.exe doesn't exist" unless the
sidecar had been staged first. That broke the release script's own cargo check
and would have broken the portable zip build too.
Renamed to tauri.installer.conf.json, which Tauri does not pick up on its own,
and passed explicitly with --config from the one step that wants it. Plain
builds are back to exactly what they were; only the installer needs staging.
