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/tcp-server/src/broadcaster.rs

@@ -1,6 +1,6 @@
 use crate::error::TcpServerError;
-use domain::{BroadcastPort, DisplayHint, Layout, WidgetId, WidgetState};
-use protocol::{ServerMessage, WidgetDescriptor, WireLayoutNode, encode};
+use domain::{BroadcastPort, DisplayHint, Layout, ThemeConfig, WidgetId, WidgetState};
+use protocol::{ServerMessage, WidgetDescriptor, WireColor, WireLayoutNode, WireTheme, encode};
 use tokio::sync::broadcast;
 
 pub struct TcpBroadcaster {
@@ -70,4 +70,26 @@ impl BroadcastPort for TcpBroadcaster {
         let frame = encode(&msg).map_err(TcpServerError::Encode)?;
         self.send_frame(frame)
     }
+
+    async fn push_theme_update(&self, theme: &ThemeConfig) -> Result<(), Self::Error> {
+        let wire_theme = domain_theme_to_wire(theme);
+        let msg = ServerMessage::ThemeUpdate { theme: wire_theme };
+        let frame = encode(&msg).map_err(TcpServerError::Encode)?;
+        self.send_frame(frame)
+    }
+}
+
+pub(crate) fn domain_theme_to_wire(t: &ThemeConfig) -> WireTheme {
+    let c = |c: &domain::ThemeColor| WireColor {
+        r: c.r,
+        g: c.g,
+        b: c.b,
+    };
+    WireTheme {
+        primary: c(&t.primary),
+        secondary: c(&t.secondary),
+        accent: c(&t.accent),
+        text: c(&t.text),
+        background: c(&t.background),
+    }
 }