Does the partner's acknowledgment, whether verbal or written, of shared ownership of the forum between him and the questioner, entail legal ownership for the questioner? And what is the ruling of Islamic law regarding the breach of the agreement concluded between them?

Transferring ownership of a portion of the forum instead of working in it is invalid due to ignorance [of its true value]. The questioner is entitled to the customary wage for the duration of his work. If they agree on him taking a copy of the files in exchange for the customary wage, it is permissible. The website owner is not allowed to breach the agreement, as Allah Almighty says: "O you who have believed, fulfill [all] contracts," and the Prophet, peace and blessings be upon him, said: "Muslims are bound by their conditions, concerning what is permissible." The advice is to fear Allah and to cooperate in resolving the dispute amicably, for Allah Almighty says: "The believers are nothing but brothers" and "So whoever pardons and makes reconciliation - his reward is due from Allah," and the Prophet, peace and blessings be upon him, said: "Do not hate one another, do not envy one another, do not turn away from one another, do not cut ties with one another, and be, O slaves of Allah, brothers."