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/protocol/src/lib.rs

@@ -2,7 +2,7 @@ mod frame;
 mod wire;
 
 pub use frame::{
-    ClientMessage, MAX_FRAME_SIZE, ServerMessage, WireColor, WireTheme, WidgetDescriptor,
+    ClientMessage, MAX_FRAME_SIZE, ServerMessage, WidgetDescriptor, WireColor, WireTheme,
     decode_client_message, decode_server_message, encode, encode_client,
 };
 pub use wire::{