feat(backend): Implement Phase 2.7 Task 1 - Medication Management System

This commit implements the complete medication management system,
which is a critical MVP feature for Normogen.

Features Implemented:
- 7 fully functional API endpoints for medication CRUD operations
- Dose logging system (taken/skipped/missed)
- Real-time adherence calculation with configurable periods
- Multi-person support for families managing medications together
- Comprehensive security (JWT authentication, ownership verification)
- Audit logging for all operations

API Endpoints:
- POST   /api/medications          - Create medication
- GET    /api/medications          - List medications (by profile)
- GET    /api/medications/:id      - Get medication details
- PUT    /api/medications/:id      - Update medication
- DELETE /api/medications/:id      - Delete medication
- POST   /api/medications/:id/log  - Log dose
- GET    /api/medications/:id/adherence - Calculate adherence

Security:
- JWT authentication required for all endpoints
- User ownership verification on every request
- Profile ownership validation
- Audit logging for all CRUD operations

Multi-Person Support:
- Parents can manage children's medications
- Caregivers can track family members' meds
- Profile-based data isolation
- Family-focused workflow

Adherence Tracking:
- Real-time calculation: (taken / total) × 100
- Configurable time periods (default: 30 days)
- Tracks taken, missed, and skipped doses
- Actionable health insights

Files Modified:
- backend/src/handlers/medications.rs - New handler with 7 endpoints
- backend/src/handlers/mod.rs - Added medications module
- backend/src/models/medication.rs - Enhanced with repository pattern
- backend/src/main.rs - Added 7 new routes

Phase: 2.7 - Task 1 (Medication Management)
Status: Complete and production-ready
Lines of Code: ~550 lines

backend/src/handlers/mod.rs

@@ -4,6 +4,7 @@ pub mod permissions;
 pub mod shares;
 pub mod users;
 pub mod sessions;
+pub mod medications;
 
 // Re-export commonly used handler functions
 pub use auth::{register, login, recover_password};
@@ -12,3 +13,4 @@ pub use shares::{create_share, list_shares, update_share, delete_share};
 pub use permissions::check_permission;
 pub use users::{get_profile, update_profile, delete_account, change_password, get_settings, update_settings};
 pub use sessions::{get_sessions, revoke_session, revoke_all_sessions};
+pub use medications::{create_medication, list_medications, get_medication, update_medication, delete_medication, log_dose, get_adherence};