Add Wine-based runner image for Windows builds

- runner/Dockerfile: Debian + Wine + Windows CPython 3.12 + PyInstaller + act_runner
- runner/entrypoint.sh: self-register with the windows:host label
- workflow windows job now builds via winpython under Wine

README.md

@@ -110,6 +110,24 @@ act_runner.exe register \
 The registration token is generated in Gitea under
 **Site Administration → Actions → Runners → Create new runner**.
 
+#### Windows builds without a Windows box (Wine runner)
+
+The `windows` job targets a runner labelled `windows` that builds under Wine on
+Linux. Build it from `runner/`:
+
+```bash
+docker build -f runner/Dockerfile -t psp-wine-runner .
+docker run -d --name psp-wine-runner --restart unless-stopped \
+  -e GITEA_INSTANCE_URL=https://git.ceaf.dev \
+  -e GITEA_RUNNER_REGISTRATION_TOKEN=<registration-token> \
+  -v /mnt/user/appdata/psp-wine-runner:/data \
+  psp-wine-runner
+```
+
+The image ships Wine + Windows CPython 3.12 + PyInstaller, and registers itself
+with the `windows:host` label. (If you have a real Windows machine instead,
+register a native `act_runner.exe` with the same `windows` label.)
+
 ## First-time setup
 
 1. Put your DAT files in `data/dats/`: