Update onboarding UI texts, buttons, and gender handling

[clemPerrousset]

This PR addresses several UI and logic updates for the Onboarding and Settings flows:

1. Gender Field Update:

   • Replaced the display label "Autre" with "Non renseigné" in the sign-up flow.
   • Updated AuthService.mapGender to correctly map "Non renseigné" (and "non renseigne") to the backend value "secret".

2. Association Onboarding Text:

   • Updated the localized string onboard_asso_info to: "Votre association ne figure pas dans la liste ? Ajoutez-la pour continuer.".

3. Onboarding/Settings Buttons & Spacing:

   • Refactored EnahancedOnboardingButtonCell to dynamically configure button titles based on context:
     • Settings: "Annuler" / "Valider".
     • Onboarding (Intermediate): "Terminer plus tard" / "Suivant".
     • Onboarding (Last Step): "Terminer plus tard" / "Terminer".
   • Reduced the sticky footer height constraint in EnhancedViewController from 130 to 90 for a more compact look.

4. Association Presentation UI:

   • Updated the title to "Présentez votre association à la communauté" and the subtitle.
   • Updated the "Description de votre association" label font to use Quicksand-Bold size 16.

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PR created automatically by Jules for task 14522611735563272698 started by @clemPerrousset

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