Share Compute (mesh-llm) is unavailable in every official Linux build — release and canary #3841

Title: Share Compute (mesh-llm) is unavailable in every official Linux build — release and canary

Body:

Share Compute fails on Linux with Couldn't check shared compute: mesh-llm feature not enabled (the stub error from desktop/src-tauri/src/mesh_llm_stubs.rs) on the current apt-installed .deb (v0.5.2).

Traced this to the release/canary CI definitions rather than a local config issue:

• mesh-llm is an opt-in Cargo feature (desktop/src-tauri/Cargo.toml): default = ["system-keyring"], with mesh-llm requiring an explicit --features mesh-llm flag.
• .github/workflows/release.yml: only the macOS job (runs-on: macos-latest, line ~181) passes --features mesh-llm. release-linux (line ~624, pnpm tauri build --verbose --ci --bundles deb,appimage ...) does not. Neither does release-windows.
• .github/workflows/linux-canary.yml (line ~173) also builds without --features mesh-llm.

So there is currently no official Linux artifact — stable or canary — that ships Share Compute at all, even though the feature and its UI are fully present and reachable in the Linux build (it just always errors).

Ask: either add a Linux release/canary variant built with --features mesh-llm (behind a separate bundle name, like the mac path already does), or gate the Share Compute UI behind a build-time flag so Linux users don't hit a dead-end error screen for a feature their build can never support.

Environment: Ubuntu (ai-local), buzz 0.5.2 via apt, binary /usr/bin/buzz-desktop.