gui-v0.4.31

• Fixed: the Linux GUI wouldn't open at all on Debian 12 Bookworm (issue
  #2). The release build ran on GitHub's ubuntu-latest, which resolves to
  Ubuntu 24.04 (glibc 2.39) — a binary linked against that refuses to even
  start on Bookworm's glibc 2.36 (GLIBC_2.38 not found), with no window
  and no visible error if launched by double-clicking rather than from a
  terminal. Now built inside a debian:bookworm container instead
  (.github/workflows/gui-build.yml's new build-linux job, kept separate
  from the windows/macos matrix job so nothing about it touches their
  config). glibc is backwards-compatible, so this maximizes how far forward
  the binary still runs rather than chasing GitHub's own runner-image
  version (which is a moving target — ubuntu-22.04 itself starts
  deprecating next month, so pinning a specific Ubuntu version wouldn't
  have been durable either). Verified: the produced binary's highest
  required glibc symbol is GLIBC_2.34, well under Bookworm's 2.36 (it was
  effectively requiring 2.39 before).

Full Changelog: gui-v0.4.30...gui-v0.4.31