feat(ci): release server and client sdk artifacts

[HeatXD]

Builds and publishes release artifacts for Server and the client SDK on windows/linux/macos, following the same shape as GekkoNet's release workflow: push to main -> per-platform build -> package -> timestamped v<date>-<sha> release.

• adds a weyvelength_client_shared target so the SDK ships as a shared library alongside the static one. the header already had the WEYVE_API / WEYVE_DLL_EXPORT plumbing, nothing was building against it. juice stays statically linked into both, so neither has extra runtime deps.
• four platforms: linux, macos, windows-msvc, windows-mingw. mingw matters because bsnes-netplay links this under mingw and an msvc .lib won't do.
• each package is bin/Server, lib/ (static + shared + windows import lib), include/weyvelength.h, LICENSE.
• tests are off in the release build and ClientExample isn't in the root CMakeLists, so neither ships. ci.yml still runs tests on PRs and main.

Verified locally under mingw: static lib, dll, import lib and Server.exe all produced, and the dll exports all 50 weyve_* symbols.

The mingw job assumes x86_64-w64-mingw32-gcc is on the runner PATH (same assumption GekkoNet makes) - unverified on the current windows-latest image, so it's fail-fast: false. Worth watching on the first run.