Add gentle French language preferences feature for educational improvements

[Copilot]

This PR implements an educational French language preference system that gently encourages more idiomatic French expressions throughout the Papillon app.

What this does

The feature analyzes text in chat messages and discussions to detect common French expressions that could be improved, such as "ça fonctionne" vs "ça marche". When less idiomatic expressions are detected, it logs gentle educational suggestions to help users learn more natural French.

Key principles

• Educational, not punitive: Provides helpful suggestions without blocking functionality
• Respectful: Users maintain full freedom to use any expressions they prefer
• Transparent: Clear logging shows suggestions for learning purposes
• Non-intrusive: Messages are sent normally, suggestions appear only in logs

Implementation

The system includes:

• Core detection utility (src/utils/language/french-preferences.ts) that identifies expressions like "ça fonctionne" and suggests "ça marche"
• Integration with chat services (src/services/chats.ts) for gentle educational logging
• Developer testing feature in DevMenu with notification examples
• Updated existing notification text to use preferred expressions
• Comprehensive documentation explaining the educational approach

Example

// When a user sends "Ça fonctionne bien !"
// The system logs: "💡 Suggestion: 'ça marche' est plus idiomatique que 'ça fonctionne'"
// But the message is still sent normally

This creates a positive learning environment that promotes good French while respecting user choice and maintaining full app functionality.

Fixes #950.

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[vexcited]

LGTM 👍

[godetremy]

Pourquoi l'app a était converti en JS ???

[Theoyeah]

Pourquoi l'app a était converti en JS ???

ca fait plus beau