chore(deps): migrate explorer styling stack to Tailwind CSS 4

[alainncls]

Summary

Upgrade the explorer styling stack to the latest eligible major versions older than 3 days as of 2026-04-23:

• tailwindcss 3.4.19 -> 4.2.2
• tailwind-merge 2.6.1 -> 3.5.0

Why this is not in the current dependency bump PR

Tailwind 4 is a breaking migration with changes to configuration, CSS entrypoints, browser support expectations, and utility generation.

Documentation

• https://tailwindcss.com/docs/upgrade-guide
• https://tailwindcss.com/blog/tailwindcss-v4

Expected codebase changes

• Review the Tailwind config and whether it should stay JS-based or move to the CSS-first model.
• Check PostCSS/CSS entrypoints and generated utility usage.
• Re-check any classes or plugin behavior affected by the v4 changes.
• Align tailwind-merge with the final utility set used by the explorer.

Migration plan

1. Run the official upgrade guide/tool on a dedicated branch.
2. Update config/CSS entrypoints for Tailwind 4.
3. Fix any utility/class regressions surfaced by the build.
4. Upgrade tailwind-merge once the Tailwind 4 class set is in place.
5. Perform visual regression testing on the explorer.

Validation checklist

• Build the explorer.
• Compare key pages visually before/after.
• Check responsive layouts, dark/light styling if applicable, and utility conflict handling.

[alainncls]

Pas de PR ouverte dans ce passage pour Tailwind 4. Le guide Tailwind v4 recommande l’upgrade tool puis une revue du diff et du rendu navigateur ; la migration peut déplacer la config vers CSS, changer PostCSS/Vite et modifier des utilitaires. Je la garde donc pour une branche UI dédiée avec validation visuelle.