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/tests/round_trip_tests.rs

@@ -1,8 +1,8 @@
 use protocol::{
     ClientMessage, ServerMessage, WidgetDescriptor, WireAlignItems, WireContainerNode,
     WireDirection, WireDisplayHint, WireDisplayHintKind, WireJustifyContent, WireKeyValue,
-    WireLayoutChild, WireLayoutNode, WireSizing, WireValue, WireWidgetState,
-    decode_client_message, decode_server_message, encode, encode_client,
+    WireLayoutChild, WireLayoutNode, WireSizing, WireValue, WireWidgetState, decode_client_message,
+    decode_server_message, encode, encode_client,
 };
 
 #[test]