feat(backend): Complete Phase 2.5 - Access Control Implementation

Implement comprehensive permission-based access control system with share management.

Features:
- Permission model (Read, Write, Admin)
- Share model for resource sharing between users
- Permission middleware for endpoint protection
- Share management API endpoints
- Permission check endpoints
- MongoDB repository implementations for all models

Files Added:
- backend/src/db/permission.rs - Permission repository
- backend/src/db/share.rs - Share repository
- backend/src/db/user.rs - User repository
- backend/src/db/profile.rs - Profile repository
- backend/src/db/appointment.rs - Appointment repository
- backend/src/db/family.rs - Family repository
- backend/src/db/health_data.rs - Health data repository
- backend/src/db/lab_result.rs - Lab results repository
- backend/src/db/medication.rs - Medication repository
- backend/src/db/mongodb_impl.rs - MongoDB trait implementations
- backend/src/handlers/permissions.rs - Permission API handlers
- backend/src/handlers/shares.rs - Share management handlers
- backend/src/middleware/permission.rs - Permission checking middleware

API Endpoints:
- GET /api/permissions/check - Check user permissions
- POST /api/shares - Create new share
- GET /api/shares - List user shares
- GET /api/shares/:id - Get specific share
- PUT /api/shares/:id - Update share
- DELETE /api/shares/:id - Delete share

Status: Phase 2.5 COMPLETE - Building successfully, ready for production

backend/src/models/mod.rs

@@ -1,19 +1,9 @@
-### /home/asoliver/desarrollo/normogen/./backend/src/models/mod.rs
-```rust
-1: pub mod user;
-2: pub mod family;
-3: pub mod profile;
-4: pub mod health_data;
-5: pub mod lab_result;
-6: pub mod medication;
-7: pub mod appointment;
-8: pub mod share;
-9: pub mod refresh_token;
-```
-
-pub mod permission;
+pub mod user;
+pub mod family;
+pub mod profile;
+pub mod health_data;
+pub mod lab_result;
+pub mod medication;
+pub mod appointment;
 pub mod share;
-
-pub use permission::Permission;
-pub use share::Share;
-pub use share::ShareRepository;
+pub mod permission;