Feat/schema patient phone validation

Description

This merge request adds strict schema-level validation to ensure data integrity for Patient entities.

The changes enforce:

• Valid Indian 10-digit phone numbers (numeric only, starting with 6–9, no country code)
• Mandatory patient_age and patient_sex fields for patient create and update operations

These validations ensure the backend remains the source of truth, complementing existing frontend checks and preventing invalid data from being created or updated via APIs.

Checklist

• The feature has been fully implemented.
• Tests for the new feature are included and passing.
• Impact on existing functionality has been considered.

Related Issue(s)

Closes #38 (closed)