Add profile conditions, scene presets, MQTT integration, and Scenes tab

Feature 1 — Profile Conditions: time-of-day, system idle (Win32
GetLastInputInfo), and display state (GUID_CONSOLE_DISPLAY_STATE)
condition types for automatic profile activation.

Feature 2 — Scene Presets: snapshot/restore system that captures target
running states, device brightness, and profile enables. Server-side
capture with 5-step activation order. Dedicated Scenes tab with
CardSection-based card grid, command palette integration, and dashboard
quick-activate section.

Feature 3 — MQTT Integration: MQTTService singleton with aiomqtt,
MQTTLEDClient device provider for pixel output, MQTT profile condition
type with topic/payload matching, and frontend support for MQTT device
type and condition editor.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/config/default_config.yaml

@@ -20,6 +20,15 @@ storage:
   picture_targets_file: "data/picture_targets.json"
   pattern_templates_file: "data/pattern_templates.json"
 
+mqtt:
+  enabled: false
+  broker_host: "localhost"
+  broker_port: 1883
+  username: ""
+  password: ""
+  client_id: "ledgrab"
+  base_topic: "ledgrab"
+
 logging:
   format: "json"  # json or text
   file: "logs/wled_controller.log"