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.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");
+    }
+}