add all crates: domain, protocol, application, client, adapters, ESP32 firmware

Server: domain (entities, value objects, ports), protocol (postcard wire types),
application (config service, data projection), adapters (config-memory, tcp-server),
bootstrap (composition root with fake data).

Client: client-domain (layout engine, render tree, HAL ports),
client-application (message handling, repaint commands),
adapters (tcp-client, display-terminal), client-desktop (end-to-end working).

ESP32: client-esp32 firmware with ILI9341 display over SPI, WiFi networking.
Display test verified on hardware — landscape orientation, text rendering works.

60 workspace tests, all passing.

crates/domain/tests/layout_tests.rs

@@ -0,0 +1,66 @@
+use std::collections::BTreeSet;
+use domain::{
+    ContainerNode, Direction, Layout, LayoutChild, LayoutNode, LayoutValidationError, Sizing,
+    WidgetId,
+};
+
+fn leaf(id: WidgetId) -> LayoutChild {
+    LayoutChild {
+        sizing: Sizing::Flex(1),
+        node: LayoutNode::Leaf(id),
+    }
+}
+
+fn row(children: Vec<LayoutChild>) -> LayoutNode {
+    LayoutNode::Container(ContainerNode {
+        direction: Direction::Row,
+        gap: 0,
+        padding: 0,
+        children,
+    })
+}
+
+#[test]
+fn validate_returns_empty_when_all_widgets_exist() {
+    let layout = Layout { root: row(vec![leaf(1), leaf(2)]) };
+    let known = BTreeSet::from([1, 2]);
+    assert!(layout.validate(&known).is_empty());
+}
+
+#[test]
+fn validate_reports_unknown_widget_ids() {
+    let layout = Layout { root: row(vec![leaf(1), leaf(99)]) };
+    let known = BTreeSet::from([1]);
+    let errors = layout.validate(&known);
+    assert_eq!(errors, vec![LayoutValidationError::UnknownWidget(99)]);
+}
+
+#[test]
+fn validate_reports_empty_container() {
+    let layout = Layout { root: row(vec![]) };
+    let known = BTreeSet::new();
+    let errors = layout.validate(&known);
+    assert_eq!(errors, vec![LayoutValidationError::EmptyContainer]);
+}
+
+#[test]
+fn validate_checks_nested_containers() {
+    let inner = LayoutChild {
+        sizing: Sizing::Flex(1),
+        node: row(vec![leaf(1), leaf(42)]),
+    };
+    let layout = Layout { root: row(vec![inner, leaf(2)]) };
+    let known = BTreeSet::from([1, 2]);
+    let errors = layout.validate(&known);
+    assert_eq!(errors, vec![LayoutValidationError::UnknownWidget(42)]);
+}
+
+#[test]
+fn widget_ids_collects_all_leaf_ids() {
+    let inner = LayoutChild {
+        sizing: Sizing::Flex(1),
+        node: row(vec![leaf(3)]),
+    };
+    let layout = Layout { root: row(vec![leaf(1), inner, leaf(2)]) };
+    assert_eq!(layout.widget_ids(), BTreeSet::from([1, 2, 3]));
+}