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/db/mongodb_impl.rs

@@ -7,6 +7,7 @@ use crate::models::{
     user::{User, UserRepository},
     share::{Share, ShareRepository},
     permission::Permission,
+    medication::{Medication, MedicationRepository, MedicationDose},
 };
 
 #[derive(Clone)]
@@ -14,6 +15,8 @@ pub struct MongoDb {
     database: Database,
     pub users: Collection<User>,
     pub shares: Collection<Share>,
+    pub medications: Collection<Medication>,
+    pub medication_doses: Collection<MedicationDose>,
 }
 
 impl MongoDb {
@@ -52,6 +55,8 @@ impl MongoDb {
                 return Ok(Self {
                     users: database.collection("users"),
                     shares: database.collection("shares"),
+                    medications: database.collection("medications"),
+                    medication_doses: database.collection("medication_doses"),
                     database,
                 });
             }
@@ -82,6 +87,8 @@ impl MongoDb {
                 return Ok(Self {
                     users: database.collection("users"),
                     shares: database.collection("shares"),
+                    medications: database.collection("medications"),
+                    medication_doses: database.collection("medication_doses"),
                     database,
                 });
             }
@@ -96,6 +103,8 @@ impl MongoDb {
         Ok(Self {
             users: database.collection("users"),
             shares: database.collection("shares"),
+            medications: database.collection("medications"),
+            medication_doses: database.collection("medication_doses"),
             database,
         })
     }
@@ -247,4 +256,49 @@ impl MongoDb {
         
         Ok(false)
     }
+    
+    // ===== Medication Methods =====
+    
+    pub async fn create_medication(&self, medication: &Medication) -> Result<Option<ObjectId>> {
+        let repo = MedicationRepository::new(self.medications.clone(), self.medication_doses.clone());
+        Ok(repo.create(medication).await?)
+    }
+    
+    pub async fn get_medication(&self, id: &str) -> Result<Option<Medication>> {
+        let object_id = ObjectId::parse_str(id)?;
+        let repo = MedicationRepository::new(self.medications.clone(), self.medication_doses.clone());
+        Ok(repo.find_by_id(&object_id).await?)
+    }
+    
+    pub async fn list_medications(&self, user_id: &str, profile_id: Option<&str>) -> Result<Vec<Medication>> {
+        let repo = MedicationRepository::new(self.medications.clone(), self.medication_doses.clone());
+        if let Some(profile_id) = profile_id {
+            Ok(repo.find_by_user_and_profile(user_id, profile_id).await?)
+        } else {
+            Ok(repo.find_by_user(user_id).await?)
+        }
+    }
+    
+    pub async fn update_medication(&self, medication: &Medication) -> Result<()> {
+        let repo = MedicationRepository::new(self.medications.clone(), self.medication_doses.clone());
+        repo.update(medication).await?;
+        Ok(())
+    }
+    
+    pub async fn delete_medication(&self, id: &str) -> Result<()> {
+        let object_id = ObjectId::parse_str(id)?;
+        let repo = MedicationRepository::new(self.medications.clone(), self.medication_doses.clone());
+        repo.delete(&object_id).await?;
+        Ok(())
+    }
+    
+    pub async fn log_medication_dose(&self, dose: &MedicationDose) -> Result<Option<ObjectId>> {
+        let repo = MedicationRepository::new(self.medications.clone(), self.medication_doses.clone());
+        Ok(repo.log_dose(dose).await?)
+    }
+    
+    pub async fn get_medication_adherence(&self, medication_id: &str, days: i64) -> Result<crate::models::medication::AdherenceStats> {
+        let repo = MedicationRepository::new(self.medications.clone(), self.medication_doses.clone());
+        Ok(repo.calculate_adherence(medication_id, days).await?)
+    }
 }