make workspace build and test reproducibly

- add Gitea sparse registry config for rmath
- commit Cargo.lock
- add default-members so host tests skip GTK/wasm frontends
- fix checkers example to use DraughtsBoard::get
- add README with prerequisites and per-frontend commands
- add Gitea CI workflow (core, wasm, wasm4, MSRV)
- fix repository metadata and stop tracking generated wasm dist

Cargo.toml

@@ -8,13 +8,16 @@ members = [
   "rdraught-sdl",
   "rdraught-ui-common",
 ]
+# Frontends requiring system libraries or a wasm target are checked explicitly.
+# See README.md for their build commands.
+default-members = ["rdraught", "rdraught-ui-common"]
 resolver = "3"
 
 [workspace.package]
 homepage = "https://gitea.woggioni.net/woggioni/rdraught"
 authors = ["Walter Oggioni <oggioni.walter@gmail.com>"]
 version = "0.1.0"
-repository = "https://github.com/gtk-rs/gtk-rs-core"
+repository = "https://gitea.woggioni.net/woggioni/rdraught"
 license = "MIT"
 edition = "2024"
 rust-version = "1.87"