build: add AppImage packaging pipeline and build scripts

packaging/appimage/Dockerfile

@@ -0,0 +1,34 @@
+FROM ubuntu:24.04
+
+COPY --from=ghcr.io/astral-sh/uv:0.10.2 /uv /uvx /usr/local/bin/
+
+ENV DEBIAN_FRONTEND=noninteractive \
+    PYTHONDONTWRITEBYTECODE=1 \
+    PYTHONUNBUFFERED=1
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    binutils \
+    ca-certificates \
+    desktop-file-utils \
+    fakeroot \
+    file \
+    libgdk-pixbuf2.0-bin \
+    libglib2.0-bin \
+    libgtk-3-bin \
+    libfuse2 \
+    librsvg2-bin \
+    patchelf \
+    python3 \
+    python3-pip \
+    python3-setuptools \
+    squashfs-tools \
+    strace \
+    xz-utils \
+    zsync \
+    && rm -rf /var/lib/apt/lists/*
+
+RUN python3 -m pip install --no-cache-dir --break-system-packages \
+    "packaging<21" \
+    appimage-builder
+
+WORKDIR /work