feat(android): add Flutter WebView app with Docker release builds

Dockerfile

@@ -0,0 +1,60 @@
+# DSH 工作台 Android 构建环境
+# 用法：
+#   docker build -t dsh-appbuilder \
+#     --build-arg http_proxy=$http_proxy --build-arg https_proxy=$https_proxy \
+#     --build-arg no_proxy=$no_proxy .
+#   ./build.sh
+#
+# 产出：build/app/outputs/flutter-apk/app-*.apk
+FROM eclipse-temurin:17-jdk-jammy
+
+ARG http_proxy
+ARG https_proxy
+ARG no_proxy
+ENV http_proxy=$http_proxy \
+    https_proxy=$https_proxy \
+    no_proxy=$no_proxy \
+    DEBIAN_FRONTEND=noninteractive \
+    ANDROID_HOME=/opt/android-sdk \
+    PUB_CACHE=/opt/pub-cache \
+    PATH=/opt/flutter/bin:/opt/android-sdk/cmdline-tools/latest/bin:/opt/android-sdk/platform-tools:$PATH
+
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends xz-utils unzip ca-certificates curl git \
+    && rm -rf /var/lib/apt/lists/*
+
+ARG FLUTTER_VERSION=3.47.7
+ARG CMDLINE_TOOLS_VERSION=13114758
+
+# Flutter SDK（固定 stable 版本，来自官方 release 归档）
+RUN curl -fsSL -o /tmp/flutter.tar.xz \
+        "https://storage.googleapis.com/flutter_infra_release/releases/stable/linux/flutter_linux_${FLUTTER_VERSION}-stable.tar.xz" \
+    && tar -xJf /tmp/flutter.tar.xz -C /opt \
+    && rm /tmp/flutter.tar.xz \
+    && git config --global --add safe.directory /opt/flutter
+
+# Android SDK cmdline-tools + 许可 + platform-tools
+RUN curl -fsSL -o /tmp/tools.zip \
+        "https://dl.google.com/android/repository/commandlinetools-linux-${CMDLINE_TOOLS_VERSION}_latest.zip" \
+    && mkdir -p "${ANDROID_HOME}/cmdline-tools" \
+    && unzip -q /tmp/tools.zip -d "${ANDROID_HOME}/cmdline-tools" \
+    && mv "${ANDROID_HOME}/cmdline-tools/cmdline-tools" "${ANDROID_HOME}/cmdline-tools/latest" \
+    && rm /tmp/tools.zip \
+    && (yes | sdkmanager --licenses > /dev/null || true) \
+    && sdkmanager "platform-tools" > /dev/null
+
+RUN flutter config --android-sdk "${ANDROID_HOME}" \
+    && flutter --disable-analytics \
+    && flutter precache --android \
+    && flutter doctor
+
+# 预热：跑一次与应用相同依赖的默认模板构建，把 Gradle 发行版/AGP/AndroidX
+# 组件、插件 AAR 和 SDK 平台下载进镜像，之后挂载源码的正式构建不再重复下载
+RUN flutter create --org dev.dsh --project-name warmup /tmp/warmup \
+    && cd /tmp/warmup \
+    && flutter pub add webview_flutter webview_flutter_android file_selector \
+    && flutter build apk --release \
+    && cd / && rm -rf /tmp/warmup \
+    && flutter doctor
+
+WORKDIR /project