status_led: show component errors only on a dedicated status LED (show_errors)

The ATOM LED gets them; displays and lights that are also normal lights don't,
so a failed component can't take them over.

common/status_led.yaml

@@ -2,6 +2,7 @@
 # Status on a visible RGB light, which stays a normal light otherwise:
 #   network down         red, slow blink
 #   no API client (HA)   orange, slow blink
+#   component error      purple, steady (only with show_errors: "true", for a dedicated status LED)
 #   OTA                  blue, fast blink; green when done, 3 red blinks on error
 #   back to normal       green for 1 s, then the light goes back to how it was
 #   packages:
@@ -12,6 +13,7 @@
 # Needs the ota id ota_esphome (common/ota_esp32.yaml).
 defaults:
   brightness: "0.3"
+  show_errors: "false"  # a failed component would take over a display or a shared light for good
 
 globals:
   - id: status_led_active
@@ -71,12 +73,15 @@ interval:
           static uint8_t tick = 0;
           tick++;
           bool slow = (tick / 2) % 2 == 0;  // 1 s on, 1 s off
-          bool problem = !network::is_connected() || !api::global_api_server->is_connected();
+          bool error = ${show_errors} && (App.get_app_state() & STATUS_LED_ERROR);
+          bool problem = !network::is_connected() || !api::global_api_server->is_connected() || error;
           if (problem) id(status_led_restore)->stop();
           if (!network::is_connected()) {
             id(status_led_show)->execute(1.0f, 0.0f, 0.0f, slow);
           } else if (!api::global_api_server->is_connected()) {
             id(status_led_show)->execute(1.0f, 0.4f, 0.0f, slow);
+          } else if (error) {
+            id(status_led_show)->execute(0.6f, 0.0f, 1.0f, true);
           } else if (id(status_led_active) && !id(status_led_restore)->is_running()) {
             id(status_led_restore)->execute(true);
           }