Local builds rebuild the WASM core when its sources change

These commands used to build the WebAssembly core only when no build existed yet. After pulling changes to the Rust crates, they kept the old build, and the web vault failed to type-check against it with errors about missing core exports.

The core’s build now records a hash of the Rust sources it was built from. The new pnpm --filter @octapass/core build:if-stale rebuilds only when that hash no longer matches, and the commands above call it every time. See development setup.