roadmap: Jan supports Tauri as an alternative build option

[louis-jan]

Problems

• Electron app size has become really big. Now, Jan has shipped a universal build, which is even bigger.
• Electron embeds Chromium and Node.js, which are not suitable for scaling to mobile platforms. See more in planning: Jan Architecture supports both Mobile and Desktop #3735

Goals

• Jan can be "packaged" to different platforms including Mobile.
• Better user installation experience.

Current Architecture

• Jan's frontend application is extensible, with core APIs and logic implementations primarily implemented from core extensions (engine management, conversational, model, cortex...). Requests from UI components to the extension's implementations.
• Application extensions can run on two different hosts: the browser and NodeJS. Need to look into it when transitioning to Tauri.
• Jan's backend is the cortex.cpp server, which processes most requests.
• There are native APIs that are bridged from the browser to the Electron main host, which run on NodeJS. E.g. setNativeTheme..

Desired Behavior

• Jan shouldn't be locked into one toolkit. Added src-tauri as an alternative bundler. Checkout refactor/support-tauri-toolkit
• Support running cortex-server as a sidecar binary for long-term operations. It currently runs as a sidecar process without a watchdog (self-restart) mechanism. We need to improve the process spawner and also support multi-architectures binary support (bundle script?).
• Distribute default llama.cpp engine variant. See feat: local engine management #4334
• Implement native commands like setNativeTheme and factoryReset. Some app functions require native APIs to work, as seen in the link provided. core/src/browser
• Deprecate Node Extension Host. It now supports only browser host, eliminating the need for multiple entries in the extension implementation. Some of these refactoring would really help:
  • roadmap: Jan has Hardware Controls and System Monitor and Prioritization #3908
  • feat: New Jan Hub UI #4170
• Deprecate the Jan server proxy to reduce the dependency on the Node host. (There's an ongoing API Server revamp issue for this.)
• CI CD for code signing, auto-updater

Additional Context

Notes:
To run from refactor/support-tauri-toolkit branch:

1. Copy cortex-server binary into src-tauri/binaries, rename it accordingly as described here https://v2.tauri.app/develop/sidecar/
2. Run yarn dev:tauri