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/adapters/config-memory/src/lib.rs

@@ -1,6 +1,6 @@
 use domain::{
-    ConfigRepository, DataSource, DataSourceId, Layout, LayoutPreset, LayoutPresetId, User,
-    WidgetConfig, WidgetId,
+    ConfigRepository, DataSource, DataSourceId, Layout, LayoutPreset, LayoutPresetId, ThemeConfig,
+    User, WidgetConfig, WidgetId,
 };
 use std::collections::HashMap;
 use std::sync::RwLock;
@@ -15,6 +15,7 @@ pub struct MemoryConfigStore {
     widgets: RwLock<HashMap<WidgetId, WidgetConfig>>,
     data_sources: RwLock<HashMap<DataSourceId, DataSource>>,
     layout: RwLock<Option<Layout>>,
+    theme: RwLock<Option<ThemeConfig>>,
     presets: RwLock<HashMap<LayoutPresetId, LayoutPreset>>,
     users: RwLock<Vec<User>>,
 }
@@ -25,6 +26,7 @@ impl Default for MemoryConfigStore {
             widgets: RwLock::new(HashMap::new()),
             data_sources: RwLock::new(HashMap::new()),
             layout: RwLock::new(None),
+            theme: RwLock::new(None),
             presets: RwLock::new(HashMap::new()),
             users: RwLock::new(Vec::new()),
         }
@@ -125,6 +127,23 @@ impl ConfigRepository for MemoryConfigStore {
         Ok(())
     }
 
+    async fn get_theme(&self) -> Result<Option<ThemeConfig>, Self::Error> {
+        let guard = self
+            .theme
+            .read()
+            .map_err(|_| MemoryConfigError::LockPoisoned)?;
+        Ok(guard.clone())
+    }
+
+    async fn save_theme(&self, theme: &ThemeConfig) -> Result<(), Self::Error> {
+        let mut guard = self
+            .theme
+            .write()
+            .map_err(|_| MemoryConfigError::LockPoisoned)?;
+        *guard = Some(theme.clone());
+        Ok(())
+    }
+
     async fn get_preset(&self, id: LayoutPresetId) -> Result<Option<LayoutPreset>, Self::Error> {
         let guard = self
             .presets