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>

src/ClawdDotNet.Web/Contracts/AutomationDtos.cs

@@ -11,3 +11,6 @@ public sealed record AutomationProposalDto(
     string Status, string? Reason, DateTime CreatedAt, DateTime? DecidedAt, long? Answers);
 
 public sealed record AutomationDecisionDto(bool Accept, string? Reason);
+
+/// <summary>#726: Whether the instance works with n8n.</summary>
+public sealed record AutomationSettingsDto(bool Enabled);

src/ClawdDotNet.Web/Endpoints/ApiEndpoints.cs

@@ -387,6 +387,18 @@ internal static class ApiEndpoints
                 p.Status, p.Reason, p.CreatedAt, p.DecidedAt, p.Answers)).ToList());
         });
 
+        // #726: whether this instance works with n8n — only then do agents propose workflows.
+        staging.MapGet("/automations/settings", (AppHost host) => Results.Ok(new AutomationSettingsDto(host.Instance.Automation.Enabled)));
+
+        staging.MapPut("/automations/settings", (AppHost host, AutomationSettingsDto input) =>
+        {
+            host.Instance.Automation.Enabled = input.Enabled;
+            host.SaveInstance(new InstanceChange(InstanceChangeKind.Settings));
+            return Results.Ok(new OutcomeDto(true, input.Enabled
+                ? "n8n connection on: agents may propose workflows, and recurring routine is put to them."
+                : "n8n connection off: no workflow proposals, no candidates."));
+        });
+
         staging.MapGet("/automations/{id:long}/workflow", async (AppHost host, long id, CancellationToken ct) =>
             host.Automations is { } automations && (await automations.ListAsync(null, 1000, ct)).FirstOrDefault(p => p.Id == id) is { } proposal
                 ? Results.Text(proposal.WorkflowJson, "application/json")