Automatisierungsvorschlaege nur mit n8n-Anbindung (#726)

An instance without n8n has no use for workflow proposals. New instance
setting automation.enabled ("this instance works with n8n"), off by default:
- off: automation_find/automation_propose refuse, no candidates are put to
  agents, and the escalation tool does not mention proposals at all;
- the switch sits in the settings card for external MCP servers; the
  approvals view says proposals are off instead of standing empty.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/ClawdDotNet.Core.Tests/Automation/AutomationProposalsTests.cs

@@ -165,6 +165,22 @@ public sealed class AutomationProposalsTests : IDisposable
         varied.ShouldNotBe(same);
     }
 
+    [Fact]
+    public async Task Without_n8n_nothing_is_proposed_and_no_candidate_is_put_to_anyone()
+    {
+        var settings = new AutomationSettings { Enabled = false };
+        var storage = new SqliteStorage(Path.Combine(_directory, "off.db"));
+        var off = new AutomationProposals(storage, _audit, _tasks, _board, NullLogger.Instance, () => settings);
+        var taskId = await RecurringTask(9);
+
+        off.Enabled.ShouldBeFalse();
+        (await off.ProposeAsync(Request(taskId), default)).Message.ShouldContain("does not work with n8n");
+        (await off.FindCandidatesAsync(default)).ShouldBeEmpty();
+
+        settings.Enabled = true;
+        (await off.ProposeAsync(Request(taskId), default)).Ok.ShouldBeTrue();
+    }
+
     [Fact]
     public void The_signature_folds_repeats_and_leaves_out_bookkeeping()
     {

tests/ClawdDotNet.Tools.Tests/Taskboard/AutomationHintTests.cs

@@ -0,0 +1,20 @@
+using ClawdDotNet.Tools.Taskboard;
+using Shouldly;
+
+namespace ClawdDotNet.Tools.Tests.Taskboard;
+
+/// <summary>#726: Agents hear of workflow proposals only in an instance that works with n8n.</summary>
+public sealed class AutomationHintTests
+{
+    [Fact]
+    public void The_hint_follows_the_n8n_switch()
+    {
+        var enabled = false;
+        var tool = new EscalationTool { AutomationEnabled = () => enabled };
+
+        tool.Description.ShouldNotContain("automation_propose");
+        enabled = true;
+        tool.Description.ShouldContain("automation_propose");
+        new EscalationTool().Description.ShouldNotContain("automation_propose", customMessage: "without the host saying so, nothing is proposed");
+    }
+}