revert: remove .env loading, restore hardcoded config

- appsettings.json: restored hardcoded secrets
- Program.cs: removed .env file loader
- Frontend api-clients: restored hardcoded localhost:5000
- Removed .env, .env.example, vite-env.d.ts files
- Kept all audit fixes (endpoints, DTOs, field names, status labels)

backend/src/HealthManager.WebApi/Controllers/AuthController.cs

@@ -5,6 +5,7 @@ using HealthManager.Application.Services;
 using HealthManager.Domain.Entities;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;
+using Microsoft.EntityFrameworkCore;
 
 namespace HealthManager.WebApi.Controllers;