chore: add AppImage release packaging

THIRD_PARTY_NOTICES

@@ -0,0 +1,44 @@
+ScanSlicer AppImage Third-Party Notices
+======================================
+
+This AppImage bundles ScanSlicer together with third-party software.
+Those components remain under their own licenses.
+
+The Python package set is resolved from the committed `uv.lock` file at
+build time. The versions listed below reflect the versions pinned in this
+repository at the time this notice was generated.
+
+Python packages bundled by the AppImage build:
+
+- PySide6 6.10.2
+  License metadata: LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+- PySide6-Addons 6.10.2
+  Distributed as part of the PySide6 runtime stack. See the PySide6 and Qt
+  license materials bundled with the wheel metadata for the exact terms.
+- PySide6-Essentials 6.10.2
+  Distributed as part of the PySide6 runtime stack. See the PySide6 and Qt
+  license materials bundled with the wheel metadata for the exact terms.
+- shiboken6 6.10.2
+  License metadata: LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+- numpy 2.4.2 (Python 3.11+) or 2.2.6 (Python < 3.11)
+  License metadata (installed Python 3.11 build): BSD-3-Clause AND 0BSD AND
+  MIT AND Zlib AND CC0-1.0
+- Pillow 12.1.1
+  License metadata: MIT-CMU
+- opencv-python 4.13.0.92
+  This package is installed from PyPI according to `uv.lock`. Consult the
+  package's bundled metadata and license files in the installed wheel for the
+  exact terms that apply to the shipped build.
+
+System packages bundled by the AppImage:
+
+- The AppImage also includes selected Ubuntu Noble runtime libraries and the
+  CPython runtime as listed in `packaging/appimage/AppImageBuilder.yml`.
+  Those components remain under their respective upstream and distribution
+  licenses.
+
+Release hygiene:
+
+- Keep this file aligned with `uv.lock` when dependency versions change.
+- Publish the corresponding source code for the exact AppImage build you ship.
+- Include the project `LICENSE` file alongside this notice.