Fix unresponsive Windows white screen

[ppXD]

What changed

• force the Windows installer to update WebView2 runtimes older than 120
• render the Wisp WebView through software composition to avoid the blank/unresponsive window seen with affected Windows 10 GPU/driver combinations
• add an opt-in frontend-ready handshake after two animation frames
• strengthen the packaged Windows smoke test so it requires a rendered Svelte frontend and a responsive normal window close, instead of merely checking that the process stays alive

Root cause

The previous smoke test treated a live process as success. A WebView2 renderer can remain running while its host window is completely white and the close button is unresponsive, which matches the reported Windows 10 failure. The installer also accepted arbitrarily old WebView2 runtimes and hardware composition remained enabled on affected graphics stacks.

User impact

Windows 10 users with stale WebView2 or problematic graphics drivers get a software-rendered, responsive Wisp UI. The speech/Vulkan compute backend remains independent of the WebView renderer.

Validation

• cargo test --manifest-path app/src-tauri/Cargo.toml — 20 passed
• svelte-check — 0 errors
• production Vite build passed
• JSON and workflow YAML parse checks passed
• cargo fmt --manifest-path app/src-tauri/Cargo.toml -- --check
• Windows packaged frontend/close smoke test will run in the PR workflow