📱(demo) make demo responsive + various component responsive improvement

[NathanVss]

The responsive version of the demo app was buggy, so we need to make it shiny!

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 426ab877370c2b41961266e7026c30dc02a350c6

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

| Name | Type | | -------------------------- | ----- | | @openfun/cunningham-react | Patch | | @openfun/cunningham-tokens | Patch |

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[jbpenrath]

There is still a little responsive bug about the onboarding modal. (The button "Let's go" has a min width set)