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/protocol/tests/round_trip_tests.rs

@@ -0,0 +1,94 @@
+use protocol::{
+    ServerMessage, ClientMessage, WidgetDescriptor,
+    WireDisplayHint, WireLayoutNode, WireContainerNode, WireLayoutChild,
+    WireDirection, WireSizing, WireWidgetState, WireKeyValue, WireValue,
+    encode, decode_server_message, encode_client, decode_client_message,
+};
+
+#[test]
+fn screen_update_round_trips() {
+    let msg = ServerMessage::ScreenUpdate {
+        layout: WireLayoutNode::Container(WireContainerNode {
+            direction: WireDirection::Row,
+            gap: 4,
+            padding: 2,
+            children: vec![
+                WireLayoutChild {
+                    sizing: WireSizing::Flex(1),
+                    node: WireLayoutNode::Leaf(1),
+                },
+                WireLayoutChild {
+                    sizing: WireSizing::Fixed(80),
+                    node: WireLayoutNode::Leaf(2),
+                },
+            ],
+        }),
+        widgets: vec![
+            WidgetDescriptor {
+                id: 1,
+                display_hint: WireDisplayHint::IconValue,
+                state: WireWidgetState {
+                    data: vec![
+                        WireKeyValue { key: "temperature".into(), value: WireValue::String("5.4°C".into()) },
+                        WireKeyValue { key: "icon".into(), value: WireValue::String("cloud_rain".into()) },
+                    ],
+                    error: None,
+                },
+            },
+        ],
+    };
+
+    let frame = encode(&msg).unwrap();
+    let payload = &frame[4..];
+    let decoded = decode_server_message(payload).unwrap();
+    assert_eq!(msg, decoded);
+}
+
+#[test]
+fn data_update_round_trips() {
+    let msg = ServerMessage::DataUpdate {
+        widgets: vec![
+            WidgetDescriptor {
+                id: 3,
+                display_hint: WireDisplayHint::TextBlock,
+                state: WireWidgetState {
+                    data: vec![
+                        WireKeyValue { key: "body".into(), value: WireValue::String("Breaking news...".into()) },
+                    ],
+                    error: None,
+                },
+            },
+        ],
+    };
+
+    let frame = encode(&msg).unwrap();
+    let payload = &frame[4..];
+    let decoded = decode_server_message(payload).unwrap();
+    assert_eq!(msg, decoded);
+}
+
+#[test]
+fn server_heartbeat_round_trips() {
+    let msg = ServerMessage::Heartbeat;
+    let frame = encode(&msg).unwrap();
+    let payload = &frame[4..];
+    let decoded = decode_server_message(payload).unwrap();
+    assert_eq!(msg, decoded);
+}
+
+#[test]
+fn client_heartbeat_round_trips() {
+    let msg = ClientMessage::Heartbeat;
+    let frame = encode_client(&msg).unwrap();
+    let payload = &frame[4..];
+    let decoded = decode_client_message(payload).unwrap();
+    assert_eq!(msg, decoded);
+}
+
+#[test]
+fn frame_has_correct_length_prefix() {
+    let msg = ServerMessage::Heartbeat;
+    let frame = encode(&msg).unwrap();
+    let len = u32::from_be_bytes([frame[0], frame[1], frame[2], frame[3]]) as usize;
+    assert_eq!(len, frame.len() - 4);
+}