muxg: release bundling and install on a fresh box

open   by a73x

`make release` builds `muxg` into the tarball but bundles none of its dynamic libraries (SDL3, freetype, fontconfig, HarfBuzz, GL), and the README says so. A fresh box that untars the release gets a `muxg` that fails to load until the user installs the right packages by hand, with no message from mux naming them. The static musl `mux` has no such step, which is one reason the TUI is the thing people actually run.

Wanted: at minimum, `muxg` prints the missing library by name and the package hint per OS; better, a documented install path per OS (Homebrew formula list, apt/pacman list) checked by `make release`; possibly an AppImage-style bundle on Linux. A gate on retiring the wall.