Add Windows cross-build and Gitea release; share CI setup

- just windows-deps / windows / package-windows: cross-compile with Odin
  objects + lld-link against an xwin SDK, static VC runtime
- Release workflow runs on v* tags, builds Linux and Windows packages,
  uploads them to the package registry and creates a Gitea release
- Shared toolchain setup as a local composite action

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -10,9 +10,15 @@ Requires [Odin](https://odin-lang.org) (dev-2026-09) and [just](https://just.sys
 just run              # build and play (debug)
 just check            # type-check with -vet
 just test             # run tests
-just package 1.0      # release build -> build/HanjaKanaMun_1.0_<os>_<arch>.tar.gz
+just package 1.0      # native release build -> build/HanjaKanaMun_1.0_<os>_<arch>.tar.gz
+just windows-deps     # Linux only: fetch Windows SDK/CRT (xwin) and raylib.lib
+just package-windows 1.0  # cross-compiled Windows build -> build/HanjaKanaMun_1.0_windows_x86_64.zip
 ```
 
+The Windows build needs `lld-link`. On macOS, `brew install lld` and set `LLD_LINK`, and point `XWIN_SDK` and
+`RAYLIB_WINDOWS` at an xwin splat and Odin's Windows `vendor/raylib/windows` folder (the Linux/macOS Odin releases
+don't include `raylib.lib`).
+
 ### Neovim
 
 `ols.json` and `odinfmt.json` configure the [ols](https://github.com/DanielGavin/ols) language server and formatter.
@@ -22,8 +28,12 @@ Formatting goes through ols (`vim.lsp.buf.format()`), or `just fmt` if `odinfmt`
 ## CI
 
 - `.gitea/workflows/gitea-build.yaml`: check, test and build on pushes and PRs to `main` and `develop`.
-- `.gitea/workflows/gitea-release.yaml`: on version branches like `1.0`, packages the Linux build and uploads it to
-  the Gitea generic package registry (`HanjaKanaMun/<version>`). Needs a `TOKEN` secret with package write access.
+- `.gitea/workflows/gitea-release.yaml`: on a version tag like `v1.0`, builds Linux and Windows packages, uploads them
+  to the Gitea generic package registry (`HanjaKanaMun/1.0`) and creates a Gitea release with both attached.
+  Needs a `TOKEN` secret with package write access.
+- `.gitea/actions/setup`: shared toolchain setup (apt packages, Odin, just).
+
+Release: `git tag v1.0 && git push origin v1.0`
 
 ## Credits