Fix Linux AppImage launch failure (libfuse2) + per-arch artifact name

[kkerti]

Problem

Since the Linux build pipeline changed, users report the AppImage failing to launch:

• Manjaro: execv error: Transport endpoint is not connected (ENOTCONN)
• Ubuntu: execv error: Input/output error (EIO)

Flatpak builds are unaffected.

Root cause

1. Legacy FUSE2 AppImage runtime. electron-builder 26.8's toolsets.appimage defaults to "0.0.0", which uses the legacy runtime (buildFuse2AppImage). That runtime dynamically links libfuse.so.2 to self-mount its embedded squashfs. Manjaro/Arch and current Ubuntu (23.10 / 24.04+) no longer ship libfuse2 by default, so the mount never comes up → accessing AppRun at the dead mountpoint returns ENOTCONN / EIO → the runtime prints execv error: <errno> before the app starts. Flatpak doesn't use the AppImage/FUSE runtime, so it was never affected.

2. artifactName missing ${arch}. The matrix builds AppImages on both ubuntu-22.04 (x64) and ubuntu-22.04-arm (arm64). The publish job downloads all artifacts into one directory with merge-multiple: true, so both builds shared the filename grid-editor-linux-<ver>.AppImage and silently overwrote each other — one arch's users could get the wrong-arch binary.

Fix

• Set toolsets.appimage: "1.0.2" (runtime 20251108). This toolset bundles the FUSE libraries inside the AppImage (usr/lib), removing the host libfuse2 dependency.
• Add ${arch} to linux.artifactName so x64/arm64 keep distinct filenames.

Auto-update: verified safe

Checked against the installed electron-updater:

• Update file is selected by extension (findFile(..., "AppImage", ...)), not by filename — the rename doesn't affect selection.
• Each arch already reads its own channel file (getChannelFilePrefix(): x64 → latest-linux.yml, arm64 → latest-linux-arm64.yml), and electron-builder regenerates those pointing at the new arch-specific files. This actually repairs the prior collision where both channels referenced a single overwritten AppImage.
• Differential (blockmap) updates keep working: the version string is substituted per update while the arch token stays constant. The first hop from an old no-arch build falls back to a full download, which is the normal safe fallback.

Note

toolsets.appimage: "1.0.2" is marked beta in electron-builder. Recommend validating a produced AppImage on a clean Manjaro / Ubuntu 24.04 box without libfuse2 installed before the release goes out.

🤖 Generated with Claude Code

[kkerti]

This PR also fixes the fact, that appimage artifacts overwrote each other without {arch} in their filename. We introduced arm builds, this caused the regression. As files were ovewritten, but electron updater yaml held correct metadata targeting specific files, this corrupted the automatic update flow.