Adding gitea build scripts for Android, Linux GUI and dockerized website

ac_web/Dockerfile

@@ -0,0 +1,52 @@
+# Serves the Flutter web build of "AC Control" as a plain static website.
+#
+# The image is self contained: it compiles the web bundle itself instead of
+# expecting a prepared `build/web` directory, so
+# `docker build -f ac_web/Dockerfile ac_web` produces exactly the same image
+# locally as the gitea action does.
+
+# ---------------------------------------------------------------- build stage
+FROM debian:bookworm-slim AS build
+
+# Keep the version in sync with `.gitea/workflows/*.yml`. The sdk is taken from
+# the official archive instead of a prebuilt flutter image, because that archive
+# has every released version and can therefore be pinned exactly.
+ARG FLUTTER_VERSION=3.44.9
+
+RUN apt-get update \
+ && apt-get install -y --no-install-recommends ca-certificates curl git unzip xz-utils \
+ && rm -rf /var/lib/apt/lists/*
+
+RUN curl -fsSL "https://storage.googleapis.com/flutter_infra_release/releases/stable/linux/flutter_linux_${FLUTTER_VERSION}-stable.tar.xz" \
+  | tar -xJ -C /opt
+
+ENV PATH="/opt/flutter/bin:${PATH}"
+
+# The flutter tool calls git on its own sdk during every command, and git
+# refuses to work in a directory it considers to belong to somebody else.
+RUN git config --global --add safe.directory /opt/flutter
+
+WORKDIR /app
+
+# The dependencies are copied on their own so that this layer is only rebuilt
+# when they actually changed, not on every source change.
+COPY pubspec.yaml pubspec.lock ./
+RUN flutter pub get
+
+COPY . .
+
+# The result is a completely static bundle - the app talks to the AcAPI from
+# the browser of the user, not from this container.
+RUN flutter build web --release
+
+# -------------------------------------------------------------- runtime stage
+FROM nginx:alpine AS runtime
+
+# The bundle is built with the backend address that is compiled into
+# `lib/main.dart`, and the browser of the visitor resolves it - not this
+# container. Serving this image to other machines therefore needs a host name
+# in `main.dart` that those machines can reach as well.
+COPY nginx.conf /etc/nginx/conf.d/default.conf
+COPY --from=build /app/build/web /usr/share/nginx/html
+
+EXPOSE 80