feat: Add remote Unsloth server support to Desktop application

[DionJones615]

This PR adds remote server support to the Unsloth Desktop application. Users can now connect to a remote backend (e.g., via Cloudflare tunnel or LAN IP) instead of always spawning the local Python sidecar.

Changes:

• Tauri CSP: Updated tauri.conf.json to allow http:, https:, ws:, and wss: for connect-src, frame-src, and media-src. Added tauri-plugin-store to the build.
• Backend CORS: Added http://127.0.0.1 to _TAURI_CORS_ORIGINS in studio/backend/utils/host_policy.py.
• Frontend Core:
  • api-base.ts: Expanded to support full remote URLs, and exported getIsRemoteMode().
  • main.tsx: Added startup hydration of remote connection state from localStorage.
• Authentication: authFetch automatically injects the remote Bearer token if isRemoteMode is active.
• Server Connection UI: Created a new UI in ConnectionsTab (connections-tab.tsx) for users to set the server URL and API token, test the connection, and persist the config.
• Process Management: Guarded use-tauri-backend.ts so start_managed_server is skipped when the remote mode is enabled, saving local memory and VRAM.
• Fixed a handful of unrelated npm run lint format errors.

Tests and linters pass successfully.

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PR created automatically by Jules for task 5409692007600219446 started by @DionJones615

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