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/data_source_tests.rs

@@ -0,0 +1,51 @@
+use std::time::Duration;
+use domain::{DataSource, DataSourceConfig, DataSourceType, DataSourceValidationError};
+
+fn make_source(source_type: DataSourceType, url: Option<&str>, poll: Duration) -> DataSource {
+    DataSource {
+        id: 1,
+        name: "test".into(),
+        source_type,
+        poll_interval: poll,
+        config: DataSourceConfig {
+            url: url.map(Into::into),
+            headers: vec![],
+            api_key: None,
+        },
+    }
+}
+
+#[test]
+fn http_json_requires_url() {
+    let source = make_source(DataSourceType::HttpJson, None, Duration::from_secs(60));
+    let errors = source.validate();
+    assert!(errors.contains(&DataSourceValidationError::UrlRequired));
+}
+
+#[test]
+fn webhook_does_not_allow_poll_interval() {
+    let source = make_source(DataSourceType::Webhook, None, Duration::from_secs(60));
+    let errors = source.validate();
+    assert!(errors.contains(&DataSourceValidationError::PollIntervalNotAllowed));
+}
+
+#[test]
+fn webhook_with_zero_interval_is_valid() {
+    let source = make_source(DataSourceType::Webhook, None, Duration::ZERO);
+    let errors = source.validate();
+    assert!(errors.is_empty());
+}
+
+#[test]
+fn poll_based_source_requires_nonzero_interval() {
+    let source = make_source(DataSourceType::Weather, Some("https://api.weather.com"), Duration::ZERO);
+    let errors = source.validate();
+    assert!(errors.contains(&DataSourceValidationError::PollIntervalRequired));
+}
+
+#[test]
+fn valid_poll_source_has_no_errors() {
+    let source = make_source(DataSourceType::Rss, Some("https://feed.example.com"), Duration::from_secs(300));
+    let errors = source.validate();
+    assert!(errors.is_empty());
+}