Add tests and implement StubBearer authentication for Signer endpoints

- Created SignerEndpointsTests to validate the SignDsse and VerifyReferrers endpoints.
- Implemented StubBearerAuthenticationDefaults and StubBearerAuthenticationHandler for token-based authentication.
- Developed ConcelierExporterClient for managing Trivy DB settings and export operations.
- Added TrivyDbSettingsPageComponent for UI interactions with Trivy DB settings, including form handling and export triggering.
- Implemented styles and HTML structure for Trivy DB settings page.
- Created NotifySmokeCheck tool for validating Redis event streams and Notify deliveries.

src/StellaOps.Notify.Connectors.Slack.Tests/SlackChannelHealthProviderTests.cs

@@ -0,0 +1,96 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using StellaOps.Notify.Engine;
+using StellaOps.Notify.Models;
+using Xunit;
+
+namespace StellaOps.Notify.Connectors.Slack.Tests;
+
+public sealed class SlackChannelHealthProviderTests
+{
+    private static readonly SlackChannelHealthProvider Provider = new();
+
+    [Fact]
+    public async Task CheckAsync_ReturnsHealthy()
+    {
+        var channel = CreateChannel(enabled: true, target: "#sec-ops");
+
+        var context = new ChannelHealthContext(
+            channel.TenantId,
+            channel,
+            channel.Config.Target!,
+            new DateTimeOffset(2025, 10, 20, 14, 0, 0, TimeSpan.Zero),
+            "trace-slack-001");
+
+        var result = await Provider.CheckAsync(context, CancellationToken.None);
+
+        Assert.Equal(ChannelHealthStatus.Healthy, result.Status);
+        Assert.Equal("true", result.Metadata["slack.channel.enabled"]);
+        Assert.Equal("true", result.Metadata["slack.validation.targetPresent"]);
+        Assert.Equal("#sec-ops", result.Metadata["slack.channel"]);
+        Assert.Equal(ComputeSecretHash(channel.Config.SecretRef), result.Metadata["slack.secretRef.hash"]);
+    }
+
+    [Fact]
+    public async Task CheckAsync_ReturnsDegradedWhenDisabled()
+    {
+        var channel = CreateChannel(enabled: false, target: "#sec-ops");
+
+        var context = new ChannelHealthContext(
+            channel.TenantId,
+            channel,
+            channel.Config.Target!,
+            DateTimeOffset.UtcNow,
+            "trace-slack-002");
+
+        var result = await Provider.CheckAsync(context, CancellationToken.None);
+
+        Assert.Equal(ChannelHealthStatus.Degraded, result.Status);
+        Assert.Equal("false", result.Metadata["slack.channel.enabled"]);
+    }
+
+    [Fact]
+    public async Task CheckAsync_ReturnsUnhealthyWhenTargetMissing()
+    {
+        var channel = CreateChannel(enabled: true, target: null);
+
+        var context = new ChannelHealthContext(
+            channel.TenantId,
+            channel,
+            channel.Name,
+            DateTimeOffset.UtcNow,
+            "trace-slack-003");
+
+        var result = await Provider.CheckAsync(context, CancellationToken.None);
+
+        Assert.Equal(ChannelHealthStatus.Unhealthy, result.Status);
+        Assert.Equal("false", result.Metadata["slack.validation.targetPresent"]);
+    }
+
+    private static NotifyChannel CreateChannel(bool enabled, string? target)
+    {
+        return NotifyChannel.Create(
+            channelId: "channel-slack-sec-ops",
+            tenantId: "tenant-sec",
+            name: "slack:sec-ops",
+            type: NotifyChannelType.Slack,
+            config: NotifyChannelConfig.Create(
+                secretRef: "ref://notify/channels/slack/sec-ops",
+                target: target,
+                properties: new Dictionary<string, string>
+                {
+                    ["workspace"] = "stellaops-sec",
+                    ["botToken"] = "xoxb-123456789012-abcdefghijklmnop"
+                }),
+            enabled: enabled);
+    }
+
+    private static string ComputeSecretHash(string secretRef)
+    {
+        var bytes = System.Text.Encoding.UTF8.GetBytes(secretRef.Trim());
+        var hash = System.Security.Cryptography.SHA256.HashData(bytes);
+        return Convert.ToHexString(hash.AsSpan(0, 8)).ToLowerInvariant();
+    }
+}