Improvements to the smart reply feature

Is your feature request related to a problem? Please describe.

Improve the way mail app provides smart replies

Describe the solution you'd like

• Implement smart replies as a text processing AI provider rather than a feature within the mail app to help integrate features to the providers like fetching additional context:
  • eg: supply the model with the schedule of the user, information from files… → reply contains suitable slots for a call
• use output validation or even restricted 'dictionaries' for the models in the providers which would force the output to conform to the specified format (like a JSON string, for example).
• Another short coming of the current freeprompt provider is that you cannot specify the system message provided to the model which limits the output quality.

Describe alternatives you've considered

No response

Additional context

cc @ChristophWurst @MB-Finski

No files or tests are named. Start by locating the current smart reply and freeprompt provider implementations, then map how providers receive context and model instructions. Done would require a provider-based design covering additional context, constrained output validation, and configurable system messages.