fix: improve workspace desktop cursor handling

[sheepbox8646]

Summary

• add a bundled desktop styling script for macOS-like XFCE sessions, including top bar, Dock/Plank, theme, icon, wallpaper, and launcher defaults
• make Xvnc hide the remote cursor at the source with -nocursor and restart old display servers that lack the flag
• keep the browser/system cursor native while carrying lightweight cursor metadata over the display data channel
• improve desktop session recovery so XFCE does not fall back to twm after logout/session loss

Root Cause

• desktop preparation did not apply the full styling path consistently across new and existing bot workspaces
• hiding cursor state was split between the remote X server and frontend CSS, which could accidentally expose the remote cursor or hide/replace the local system cursor
• stale or partial desktop sessions could survive without a healthy XFCE session/window manager

Validation

• go test ./internal/display ./cmd/bridge ./internal/handlers
• pnpm exec eslint apps/web/src/pages/home/components/display-pane.vue
• sh -n scripts/desktop-style.sh && sh -n scripts/desktop-install.sh && git diff --check && git diff --cached --check
• pre-commit hook: full Go test and Go lint passed during commit

[sheepbox8646]

Superseded by split PRs: #609 for cursor optimization and #610 for desktop customization.