fix(desktop): map GNOME X11 window before Mutter management - #5435

Summary

• add a Linux-only GTK startup path that maps the hidden window once with override_redirect, then remaps it under Mutter management
• skip saved window-state restoration on Linux to avoid racing the initial hidden map
• ship an opaque, normal-size, frameless Linux window configuration with client-side minimize, maximize/restore, and close controls
• leave macOS and Windows startup behavior unchanged

Root cause

On an NVIDIA DGX Spark running Ubuntu 24.04 with GNOME/X11, Mutter accepted Buzz's correctly sized GTK client but immediately left it in WM_STATE=Iconic and Map State: IsUnMapped. Calls to show, unminimize, focus, delayed reveal, opaque rendering, and the existing WebKit safe-rendering settings did not map it.

Realizing the hidden GTK ApplicationWindow, performing its first map outside window-manager redirection, and handing it back to Mutter after 100 ms produced a normal managed window. Native decorations reintroduced the Iconic state on the affected system, so the Linux configuration uses application chrome.

This addresses the GNOME/X11 mapping path reported in #2811. The original Fedora/Skia transparent-window report may have a separate rendering cause, so this PR does not close the broader issue.

User impact

Affected Linux users get a visible, taskbar-managed window with working focus, movement, resizing, minimize/maximize, close, and Alt-F4 behavior. Linux starts at a normal size rather than restoring saved maximized state; macOS and Windows continue restoring window state.

The ARM64 sidecar packaging issue noted in the field report is intentionally out of scope.

Validation

• cargo fmt --manifest-path desktop/src-tauri/Cargo.toml --all -- --check
• cargo check --manifest-path desktop/src-tauri/Cargo.toml --lib
• pnpm -C desktop exec biome check src/app/AppTopChrome.tsx
• pnpm -C desktop typecheck
• pnpm -C desktop build
• pnpm -C desktop check:file-sizes
• equivalent production ARM64 patch previously installed and verified on one DGX Spark: IsViewable, WM_STATE=Normal, override redirect disabled after remap, onboarding completed

Signed-off-by: Neo Days Off neodaysoff@users.noreply.github.com