Add support for MUI v7

[djhi]

Problem

MUI v7 is out.

Solution

Follow #10655

• Update peer dependencies to include MUI v7
• Use MUI v7 in the ecommerce demo
• Keep the tutorial in v6

How To Test

• make run-demo and compare it with https://marmelab.com/react-admin-demo
• also test the new CssVariables theme in the demo
• make run-tutorial

To make sure the demo builds despite the @ts-expect-error here:

• copy the demo somewhere outside the monorepo
• add resolutions just like we do with create-react-admin but targets MUIv7:

"resolutions": {
        "@emotion/react": "^11.14.0",
        "@emotion/styled": "^11.14.0",
        "@mui/icons-material": "^7.0.0",
        "@mui/material": "^7.0.0",
        "react": "^19.0.0",
        "react-dom": "^19.0.0",
        "react-router": "^7.1.3",
        "react-router-dom": "^7.1.3"
},

• copy the monorepo packages in the demo node_modules
• Build the demo

Additional Checks

• The PR targets master for a bugfix or a documentation fix, or next for a feature

[djhi]

Question: should we update the create-react-admin template too? @fzaninotto @slax57 @erwanMarmelab?

[slax57]

Other than that I found no issues while testing, well done!

Regarding your question about create-react-admin, yes I believe we should update the version in the templates (but please in another PR, this one's already big enough 😅 )