AppImage was dropped earlier when linuxdeploy's AppImage runtime
couldn't FUSE-mount on GH Actions runners. Now viable again because:
1. `APPIMAGE_EXTRACT_AND_RUN=1` bypasses FUSE (extract-and-run).
2. The thin uv-venv installer is ~10 MB (vs the prior ~2 GB PyInstaller
payload that tripped linuxdeploy's internal size limits).
Matrix `bundles` for Linux: `deb,updater` → `deb,appimage,updater`.
tauri.conf.json `targets` also updated so dev builds can produce
AppImages locally.
Covers universal Linux — runs on any glibc-2.31+ host without a
package manager.
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
