Feature Request: (webui) Implement a experimental features on webui

[ngxson]

List for experimental functions:

• Allow edit assistant message
• Allow upload txt and code files (+ drag n drop)
• PDF parsing
• Model context protocol (discussed in another PR)
• Equivalent of "canvas" on claude / chatgpt
• On-browser python (Pyodide)
• Or even the whole linux emulator on-browser (WebVM), not sure if this is even usable

Feature Description

• Add a new "experimental functions" under settings menu
• Add an API for contributors to add their new functionalities without touching too many other parts
• Some packages will now be loaded from CDN to prevent too much bloat into the main bundle

Motivation

New functions like #11647 requires to add a big package and may not just half-working. One way that I can think of is to distribute it firstly as experimental function, gather feedback and when user really love it, we can decide to move it into the main bundle.

Possible Implementation

Probably need to firstly move to ReactJS, as VueJS code base now looks too messy.