However, EU law dictates that every person in the EU should have the right to work and earn a living - this is an absolute fundamental principal and countries / companies are not allowed to have contracts that contravene this right. If they do, then they are rarely legal.
As I've already mentioned, French employment contracts are not made up as they go along. They have to conform to the Code du Travail and had the OP had any problem with the clause within it he should have not signed it, checked with the Inspecteur du Travail that it was legal as defined by the Code du Travail (which it will have been) and it if was, he shouldn't have signed it if he wasn't happy with it. Having signed it, he is now legally obliged to adhere to it.
I am absolutely sure of my facts about FRENCH employment contracts having restrictive/prohibitive clauses within them. My previous gérant was a lawyer and adhered very strictly to the Code du Travail and everything legal. Within most 'specialist' or 'sales' contracts there will be some clause regarding working elsewhere either geographically and/or time specified (as is the case for the OP).
Just a simple Google search reveals lots of information about this and specifically within France. As ever with case law, the most likely outcomes are always heavily influence by other similar rulings and I found these webpages which explain it quite well: http://www.iln.com/bullet_iln_three_one/lefevre_article_two.htm and http://www.acc.com/legalresources/publications/topten/Non-compete-Clauses-in-Europe.cfm.
There's no point whatsoever looking at case law outside of France. Couldn't open your link but anyway it wasn't to an official or other French website quoting the rights under the Code du Travail so will have been presumably irrelevant. Try this instead:
This phrase is particularly relevant:: clause de non-concurrence : par cette clause, l'employé s'engage à ne pas travailler pour une entreprise du même secteur d'activité, dans une zone géographique définie et dans un temps limité, après son licenciement ou sa démission ; elle doit faire l'objet d'une contrepartie financière4.
The point is, a non-compete clause can ONLY be legal if the company can reasonably show that you working for a competitor is damaging to it's own business. Nobody can stop you working for a competitor if this is not the case, because this contravenes your right to work and earn a living. "A CNC may not unreasonably limit the possibilities of the employee to find a new employment."
Not so. In France an employer DOES NOT have to prove an ex-employer (or self-employed person contracted with them) is damaging to its own business. The ex-employee is bound within the clause and it suffices for the Prudhommes to regard the new employment contract to justify that the clause has been broken. If an employer wishes to waive this clause on severance, they do so in writing to the employee. If there is a geographical clause for example for a self-employed estate agent not to work for another agent within six months, they can't. Simples. Going back to the OP, if you can pick the bones out of what I am trying to explain, under your French employment contract you have signed to accept that you won't design for a competitor upon severance of your contract and that's the legal stance I'm afraid. You can find another employment contract but you can't do the job specified as an exclusive clause within your contract. It would help if you pm'd me with the precise wording from your contract of this clause.
I'm not a lawyer but I have spend a lot of time studying incidents of non-compete clauses and their validity. Of course, if you have any doubt then you should go to see a lawyer for clarification. If you have home / house insurance, sometimes they will cover you for some legal advice in these matters. But just because your contract might be written by a company's expert "comptable" I would not take it as gospel, I have seen MANY employment contracts that have illegal covenants in them - it is well known that companies leave them in as a scare-tactic.
In France?? If not, you need to understand it's totally different here. To the OP - you do not need to see a lawyer, you need to see an Inspecteur du Travail. Scare-tactics don't exist in French employment contracts by the way! It's all governed and regulated very strictly by the Code du Travail.