Papercuts and features

[teolemon]

Problem

### Issues spotted during UX review
- [ ] in export : a pull request can be created the first time but can’t be modified next (user should be able to add a commit)
- [ ] PR created from editor should not be modified via Github directly (add a warning in the PR)
- [x] Error page : add a warning to tell user to fix them manually via Github (not the editor)
- [x] Error page : can’t see the entire error (character-limited text area)
- [ ] Existing project : add creation date of a project
- [ ] Allow exporting commits
- [ ] PRs are not generated on the correct repository.
- [ ] Add simple authentication on the Taxonomy Editor to avoid spam.
- [ ] Parsing errors should be actionable.
- [ ] Product Opener does not have a test that detects duplicates in taxonomies
- [ ] When an error is detected during analysis, a solution or resolution method is proposed (even if it is, eg: correct on GitHub, merge, and import the tax again).
- [ ] Indicate on the pull requests generated that they should not be modified from GitHub but directly from the “taxonomy editor” with a link to it or directly a deep link to the project in question on the Taxonomy Editor
- [ ] Add the text in the “Add a new node” button.
- [ ] Add the creation date to the list of projects.
- [ ] Miller columns to view different levels of nodes (and edit a node on the same page) ? or like IDE with toggle lists ?

### Technical debt feedback
- [ ] on ne sait pas ce que renvoie l’API Fast API (ajouter des checks ?)
- [ ] UseEffect - hook qui est partout et qui est un anti-pattern
- [ ] Certains fichiers excessivement compliqués
- [ ] Le code du parsing est pas clair, malgré les commentaires
- [ ] Question de la gestion des transactions (trop souvent des transactions)
- [ ] Question des variables globales (anti-pattern ?)
- [ ] Code plus idiomatique. Pas trop de commentaires, plutôt du code idiomatique
- [ ] Travail sur les noms de variables pour les clarifier
- [ ] Pas de linting sur le frontend eslint
- [ ] Typage statique sur le paquet python

### For later
- [ ] Add a dark mode to taxonomy-editor