feat(worker): add hub methods for list and task agent settings

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/ClaudeDo.Worker.Tests/Hub/AgentSettingsHubTests.cs

@@ -0,0 +1,47 @@
+using ClaudeDo.Data.Models;
+using ClaudeDo.Data.Repositories;
+using ClaudeDo.Worker.Tests.Infrastructure;
+using Xunit;
+
+namespace ClaudeDo.Worker.Tests.Hub;
+
+public sealed class AgentSettingsHubTests : IDisposable
+{
+    private readonly DbFixture _db = new();
+    private readonly ClaudeDo.Data.ClaudeDoDbContext _ctx;
+    private readonly ListRepository _repo;
+
+    public AgentSettingsHubTests()
+    {
+        _ctx = _db.CreateContext();
+        _repo = new ListRepository(_ctx);
+    }
+
+    public void Dispose()
+    {
+        _ctx.Dispose();
+        _db.Dispose();
+    }
+
+    [Fact]
+    public async Task UpdateListConfig_AllNull_DeletesRow()
+    {
+        var listId = Guid.NewGuid().ToString();
+        await _repo.AddAsync(new ListEntity { Id = listId, Name = "L", CreatedAt = DateTime.UtcNow });
+        await _repo.SetConfigAsync(new ListConfigEntity
+        {
+            ListId = listId, Model = "opus", SystemPrompt = null, AgentPath = null,
+        });
+
+        string? model = null, sp = null, ap = null;
+        if (model is null && sp is null && ap is null)
+            await _repo.DeleteConfigAsync(listId);
+        else
+            await _repo.SetConfigAsync(new ListConfigEntity
+            {
+                ListId = listId, Model = model, SystemPrompt = sp, AgentPath = ap,
+            });
+
+        Assert.Null(await _repo.GetConfigAsync(listId));
+    }
+}