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/client-application/src/client_app.rs

@@ -1,7 +1,7 @@
 use client_domain::{BoundingBox, Color, LayoutEngine, RenderTree, ThemeConfig};
 use domain::LayoutNode;
 use protocol::{
-    ServerMessage, WireColor, WidgetDescriptor, WireDisplayHint, WireLayoutNode, WireWidgetState,
+    ServerMessage, WidgetDescriptor, WireColor, WireDisplayHint, WireLayoutNode, WireWidgetState,
 };
 use std::collections::HashMap;