extract api-types crate, adopt thiserror for all errors

api-types: standalone crate with DTOs (widget, data source, layout, preset)
extracted from http-api. Shared between http-api and future SPA.

thiserror: replaced all manual Display impls with derive macros across
8 crates (config-sqlite, config-memory, tcp-server, tcp-client,
http-json, rss, media, application).

crates/adapters/config-memory/src/lib.rs

@@ -6,19 +6,12 @@ use domain::{
     WidgetConfig, WidgetId,
 };
 
-#[derive(Debug)]
+#[derive(Debug, thiserror::Error)]
 pub enum MemoryConfigError {
+    #[error("lock poisoned")]
     LockPoisoned,
 }
 
-impl std::fmt::Display for MemoryConfigError {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            MemoryConfigError::LockPoisoned => write!(f, "lock poisoned"),
-        }
-    }
-}
-
 pub struct MemoryConfigStore {
     widgets: RwLock<HashMap<WidgetId, WidgetConfig>>,
     data_sources: RwLock<HashMap<DataSourceId, DataSource>>,