Validate example dev experience on Linux VM

[joeblew999]

Goal

Use the existing Linux VM infrastructure (linux-test, linux-build) to validate that the Tauri examples work for developers who are natively on Linux — not just cross-compiling from Mac.

What to validate

Onboarding (linux-test — clean Ubuntu)

• mise run init + mise run setup installs all deps correctly
• No Mac-specific assumptions in the setup path

Dev loop (linux-build)

• cargo tauri dev runs successfully (headless via xvfb or virtual display)
• Hot reload works
• Screenshot task works (WebDriver + virtual display)

Build

• mise run vm:build linux-build produces .deb and .AppImage
• Built artifacts install and run on linux-test (clean machine)

Why

We already have the VM infrastructure. Using it to also cover the Linux dev experience means we catch issues before Linux users hit them.