theme config, layout preview, container alignment

Server: ThemeConfig entity + CRUD (GET/PUT /theme), SQLite persistence,
ThemeUpdate broadcast to ESP32 on save and initial connect.
Client: render engine uses theme colors, full-screen redraw on theme change.
SPA: theme page with color pickers + presets, layout preview with TS port
of layout engine, justify/align controls on containers.
DisplayHint refactored to struct (kind + h_align + v_align).

crates/application/tests/config_service_tests.rs

@@ -3,8 +3,8 @@ mod support;
 use application::ConfigService;
 use domain::{
     AlignItems, ConfigRepository, ContainerNode, DataSource, DataSourceConfig, DataSourceType,
-    Direction, DisplayHint, DisplayHintKind, DomainEvent, JustifyContent, KeyMapping, Layout, LayoutChild,
-    LayoutNode, LayoutPreset, Sizing, WidgetConfig,
+    Direction, DisplayHint, DisplayHintKind, DomainEvent, JustifyContent, KeyMapping, Layout,
+    LayoutChild, LayoutNode, LayoutPreset, Sizing, WidgetConfig,
 };
 use std::time::Duration;
 use support::{InMemoryConfigRepository, InMemoryEventPublisher};