Why did you put all the garbage of .less/.svg which is not use as I can see in the code, only the compiled css + compiled font is used (like 10 files at max).
1. Commit != CTRL+S
2. Commit message should be clear about what it fix/update
3. Stop merge commit on all this versioning ecosystem which not usefull at all
4. Everytime a file is edit, CLEAN IT remove all tabs => space
5. Everytime a function is edit use variable with proper names, not test, thing, object, blabla...
6. Rename table name, all in english, rename inconsistency field example : (facture->facnumber, facture_fourn->ref)
7. Stop any other new development before everything which is available really work, like accountancy
8. It's not possible to refactor (less work to redo everything), but keep old code style clean as much as possible will be a start.
9. I actually manage teamworkers on development projects, and like I said often, let MySQL do the work for you as much as possible, so when you do query like for VAT functions, do the simple math directly in MySQL, all the code of MySQL is reviewed/controlled and each fonction is optimised as much as possible, you will never (or in rare case) bit them on that task, so do it in SQL cleaner/faster :).
11. Avoid multi copy of the same code
12. Wrong usage of jdate( it should be link to sql result object not db object, which make it a pain to use, because of the need to make db instance follow dataset.