feat: Configurable Heart Rate Zone calculation methods

[SoNdA11]

Description:
Currently, heart rate might rely on generic formulas. We need to allow users to configure how their HR zones are calculated in their profile to provide accurate physiological feedback.

Acceptance Criteria:

• Add input fields in the user profile for Max HR and Resting HR.
• Support Zone calculation using the standard formula (e.g., % of Max HR, estimated via 220-age if not provided).
• Support Zone calculation using the Karvonen formula (Heart Rate Reserve).
• Ensure the selected method dynamically updates the UI zones during the ride.