Fold server 0.3.1

Linux x64 standalone server and bundled web client, built locally from 9db9535c3c. Includes the npm-compatible tarball for older launchers. SHA256SUMS covers both packages.

Validation: standalone version and HTTP smoke checks passed; isolated npm installation reports 0.3.1 and service preflight reports ready with launcher protocol 3.

Upgrade note: this release requires service launcher protocol 3. Servers using an older launcher must update the launcher on the server machine before a managed update can proceed; preflight blocks incompatible launchers.