Show a slack target's retry setting in the target list (closes #395)

The target list showed only the masked webhook URL for a slack
target, though its edit page saves a retry setting and delivery
honours it. It now shows the same retry fields, with the same
labels and wording, as an http target.

Model: opus-5-5

internal/delivery/target_config_view_test.go

@@ -158,7 +158,10 @@ func TestNewTargetViews_DeletedTarget(t *testing.T) {
 	)
 	assert.Equal(
 		t,
-		map[string]string{"Webhook URL": slackMaskedURL},
+		map[string]string{
+			"Webhook URL": slackMaskedURL,
+			"Max Retries": "0 (fire-and-forget)",
+		},
 		fieldMap(view.Config),
 	)
 }
@@ -189,7 +192,32 @@ func TestNewTargetViews_Slack(t *testing.T) {
 
 	assert.Equal(
 		t,
-		map[string]string{"Webhook URL": slackMaskedURL},
+		map[string]string{
+			"Webhook URL": slackMaskedURL,
+			"Max Retries": "0 (fire-and-forget)",
+		},
+		fieldMap(view.Config),
+	)
+}
+
+// TestNewTargetViews_SlackRetries proves a Slack target shows
+// its retry settings the same way an HTTP target does.
+func TestNewTargetViews_SlackRetries(t *testing.T) {
+	t.Parallel()
+
+	target := slackTarget()
+	target.MaxRetries = 2
+	target.MaxQueueSize = 100
+
+	view := viewFor(t, target)
+
+	assert.Equal(
+		t,
+		map[string]string{
+			"Webhook URL":    slackMaskedURL,
+			"Max Retries":    "2",
+			"Max Queue Size": "100",
+		},
 		fieldMap(view.Config),
 	)
 }