Add discovery freshness to the local/full context formatter

formatSingleDiscovery (the local/full path, FormatForAIContext) reported a
resource's service, access, paths, and ports but not how old the discovery was —
so Ollama/local users lacked the recency signal cloud users just got. Emit a
"Last Discovered: <age>" header fact when the timestamp is known, completing
freshness parity across the cloud-safe and full paths. Omitted when unknown.

Test: TestFormatSingleDiscovery_IncludesFreshness (present when set, absent when
zero).

internal/servicediscovery/formatters.go

@@ -118,6 +118,12 @@ func formatSingleDiscovery(d *ResourceDiscovery) string {
 	sb.WriteString(fmt.Sprintf("- **Type:** %s\n", d.ResourceType))
 	sb.WriteString(fmt.Sprintf("- **Target:** %s\n", firstNonEmpty(d.Hostname, d.TargetID)))
 
+	// Freshness so the model (local/full path) can caveat staleness rather than
+	// presenting a cached scan as current — parity with the cloud-safe path.
+	if !d.UpdatedAt.IsZero() {
+		sb.WriteString(fmt.Sprintf("- **Last Discovered:** %s\n", FormatDiscoveryAge(d)))
+	}
+
 	if d.ServiceVersion != "" {
 		sb.WriteString(fmt.Sprintf("- **Version:** %s\n", d.ServiceVersion))
 	}

internal/servicediscovery/formatters_test.go

@@ -329,3 +329,21 @@ func TestFormatCloudSafeContext(t *testing.T) {
 		t.Errorf("cloud-safe context must report discovery age\n--- output ---\n%s", freshOut)
 	}
 }
+
+func TestFormatSingleDiscovery_IncludesFreshness(t *testing.T) {
+	d := &ResourceDiscovery{
+		ID:           MakeResourceID(ResourceTypeSystemContainer, "node1", "101"),
+		ResourceType: ResourceTypeSystemContainer,
+		ServiceName:  "Home Assistant",
+	}
+	// No timestamp -> no freshness line (parity with the cloud-safe path).
+	if strings.Contains(formatSingleDiscovery(d), "Last Discovered:") {
+		t.Fatalf("expected no freshness line when UpdatedAt is zero")
+	}
+	// Known timestamp -> the local/full path reports discovery age.
+	d.UpdatedAt = time.Now().Add(-3 * time.Hour)
+	out := formatSingleDiscovery(d)
+	if !strings.Contains(out, "**Last Discovered:** 3 hours ago") {
+		t.Fatalf("expected freshness line in single-discovery output, got:\n%s", out)
+	}
+}