fix(tauri): Set WEBKIT_DMABUF_RENDERER_FORCE_SHM=1 to avoid nvidia graphics bug at no performance cost

[lgray]

WEBKIT_DMABUF_RENDERER_FORCE_SHM=1 on linux machines to avoid blank-screen, but keep acceleration, with nvidia graphics drivers. Without this tauri renders a blank screen, and the game is near unplayable without GPU acceleration, so WEBKIT_DISABLE_DMABUF_RENDERER=1 is not the correct solution.

This PR adds a line to the Tiltfile to ensure this environment variable is set.

[gemini-code-assist]

Code Review

This pull request configures the WEBKIT_DMABUF_RENDERER_FORCE_SHM environment variable in the Tiltfile for the Tauri local resource to force shared-memory buffers and avoid GPU-path glitches. Feedback indicates that setting this environment variable in the Tiltfile only resolves the issue during local development, and recommends setting it programmatically in the Rust entry point of the Tauri application to ensure production builds are also protected against the blank-screen Nvidia bug.

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[lgray]

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Addressed the review guidance: the env var is now set programmatically in phase_tauri::run() (7c6f8a7) — before the first webview is created, compile-gated #[cfg(target_os = "linux")], and only when the variable isn't already present so an operator's value wins. The Tiltfile setting is removed in the same commit: with the fix in-app, dev builds (pnpm tauri:dev) exercise the exact code path production ships, instead of masking it behind a dev-only env.

Verification: cargo check and cargo clippy -- -D warnings clean on the phase-tauri crate; cargo fmt applied; pre-commit parser gates PASS (no engine/parser surface touched).