Revert broken desktop release changes

[weidu12123]

Summary

• Revert the desktop packaging merge because it was based on an incomplete release package and changed the web layout.
• Keep the repository main branch aligned with the known-good v4.0.0 source state.

Test plan

• Release cleanup was handled separately by deleting the incorrect desktop/macOS/beginner assets.

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Summary by cubic

Reverts the broken desktop packaging merge and returns the app to the known‑good v4.0.0 web state. Removes Electron/Tauri artifacts and restores the web layout and login gate.

• Bug Fixes

  • Restored web-only auth flow (no desktop bypass) and re-added the “Hosts” nav.
  • Removed desktop-only UI and bridge code (desktop tab in settings, frontend/src/utils/desktop.ts, and related emits).

• Dependencies

  • Dropped desktop packaging and tooling: removed electron, electron-builder, @tauri-apps/cli, desktop scripts, and .github/workflows/release-macos.yml.
  • Reset app entry to server.js and cleaned package-lock.json.

^{Written for commit 7b5665c. Summary will update on new commits. Review in cubic}