Fix WASM timeout and add opt-in serialization
Remove the fixed 10-second operation timeout that was too short for
1Password SDK WASM cold starts. Use signal-driven context cancellation
instead so SIGTERM/SIGINT properly abort in-flight operations.
Replace the mandatory blocking lock with an opt-in --serialize flag
that uses non-blocking flock polling with timeout, periodic logging,
and context cancellation. This lets resource-constrained machines
serialize concurrent invocations without penalizing capable ones.
Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com