feat(health): add custom DB, Qdrant, and Neo4j health check services and secure Qdrant in staging

src/NexusReader.Web/Services/DatabaseHealthCheck.cs

@@ -0,0 +1,35 @@
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+using NexusReader.Data.Persistence;
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace NexusReader.Web.Services;
+
+public class DatabaseHealthCheck : IHealthCheck
+{
+    private readonly AppDbContext _dbContext;
+
+    public DatabaseHealthCheck(AppDbContext dbContext)
+    {
+        _dbContext = dbContext;
+    }
+
+    public async Task<HealthCheckResult> CheckHealthAsync(
+        HealthCheckContext context, CancellationToken cancellationToken = default)
+    {
+        try
+        {
+            var canConnect = await _dbContext.Database.CanConnectAsync(cancellationToken);
+            if (canConnect)
+            {
+                return HealthCheckResult.Healthy("Database is accessible.");
+            }
+            return HealthCheckResult.Unhealthy("Cannot connect to the database.");
+        }
+        catch (Exception ex)
+        {
+            return HealthCheckResult.Unhealthy("Database health check failed with exception.", ex);
+        }
+    }
+}