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

runner/Dockerfile

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+# Wine-based Gitea Actions runner: builds Windows binaries on a Linux host.
+#
+# Jobs run in "host" mode inside this container, where a Windows CPython 3.12
+# (running under Wine) plus PyInstaller produce the .exe. Node.js and git are
+# included so the stock JS actions (actions/checkout, actions/upload-artifact)
+# work as-is.
+FROM debian:bookworm-slim
+
+ENV DEBIAN_FRONTEND=noninteractive \
+    WINEPREFIX=/root/.wine \
+    WINEDEBUG=-all \
+    WINEDLLOVERRIDES="mscoree,mshtml=" \
+    PYTHON_VERSION=3.12.8
+
+# Wine (64-bit), node + git for JS actions, and build/package tooling.
+RUN apt-get update && apt-get install -y --no-install-recommends \
+        ca-certificates curl wget unzip zip \
+        wine wine64 xvfb winetricks cabextract \
+        nodejs git \
+    && apt-get clean && rm -rf /var/lib/apt/lists/*
+
+# Gitea Actions runner (linux-amd64 binary).
+RUN wget -qO /usr/local/bin/act_runner \
+      "https://gitea.com/gitea/act_runner/releases/download/v0.6.1/act_runner-0.6.1-linux-amd64" \
+    && chmod +x /usr/local/bin/act_runner
+
+# Windows CPython 3.12, silent install into C:\Python312.
+RUN wget -qO /tmp/python-installer.exe \
+      "https://www.python.org/ftp/python/${PYTHON_VERSION}/python-${PYTHON_VERSION}-amd64.exe" \
+    && xvfb-run -a wine /tmp/python-installer.exe \
+        /quiet InstallAllUsers=1 PrependPath=1 Include_test=0 Include_launcher=0 Shortcuts=0 \
+    && rm -f /tmp/python-installer.exe \
+    && wine "C:\\Python312\\python.exe" --version
+
+# MSVC runtime required by PySide6's Qt DLLs.
+RUN xvfb-run -a winetricks --unattended vcrun2022
+
+# Convenience wrapper: winpython -> wine C:\Python312\python.exe
+RUN printf '#!/bin/sh\nexec wine "C:\\Python312\\python.exe" "$@"\n' > /usr/local/bin/winpython \
+    && chmod +x /usr/local/bin/winpython
+
+# Pre-install the Windows build deps so CI jobs start fast.
+COPY requirements-build.txt /tmp/requirements-build.txt
+RUN winpython -m pip install --upgrade pip \
+    && winpython -m pip install -r /tmp/requirements-build.txt \
+    && rm -f /tmp/requirements-build.txt
+
+COPY runner/entrypoint.sh /usr/local/bin/entrypoint.sh
+RUN chmod +x /usr/local/bin/entrypoint.sh
+
+WORKDIR /data
+ENTRYPOINT ["/usr/local/bin/entrypoint.sh"]

runner/entrypoint.sh

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+#!/bin/sh
+set -e
+
+# Register on first run, then run the daemon (host mode).
+if [ ! -f /data/.runner ]; then
+    echo "Registering Wine runner with Gitea…"
+    act_runner register --no-interactive \
+        --instance "${GITEA_INSTANCE_URL:?GITEA_INSTANCE_URL is required}" \
+        --token "${GITEA_RUNNER_REGISTRATION_TOKEN:?GITEA_RUNNER_REGISTRATION_TOKEN is required}" \
+        --name "${RUNNER_NAME:-windows-builder}" \
+        --labels "${RUNNER_LABELS:-windows:host}"
+fi
+
+exec act_runner daemon