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/src/config_service.rs

@@ -1,6 +1,6 @@
 use domain::{
     ConfigRepository, DataSource, DataSourceId, DataSourceValidationError, DomainEvent,
-    EventPublisher, Layout, LayoutPreset, LayoutPresetId, WidgetConfig, WidgetId,
+    EventPublisher, Layout, LayoutPreset, LayoutPresetId, ThemeConfig, WidgetConfig, WidgetId,
 };
 use std::fmt;
 
@@ -142,6 +142,21 @@ where
         Ok(())
     }
 
+    pub async fn update_theme(
+        &self,
+        theme: ThemeConfig,
+    ) -> Result<(), ConfigError<C::Error, E::Error>> {
+        self.config
+            .save_theme(&theme)
+            .await
+            .map_err(ConfigError::Repository)?;
+        self.events
+            .publish(DomainEvent::ThemeChanged { theme })
+            .await
+            .map_err(ConfigError::Event)?;
+        Ok(())
+    }
+
     pub async fn save_preset(
         &self,
         preset: LayoutPreset,