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/application/src/config_service.rs

@@ -11,25 +11,18 @@ pub struct ConfigService<'a, C, E> {
     events: &'a E,
 }
 
-#[derive(Debug)]
+#[derive(Debug, thiserror::Error)]
 pub enum ConfigError<C: fmt::Debug, E: fmt::Debug> {
+    #[error("repository error: {0:?}")]
     Repository(C),
+    #[error("event error: {0:?}")]
     Event(E),
+    #[error("validation errors: {0:?}")]
     Validation(Vec<DataSourceValidationError>),
+    #[error("not found")]
     NotFound,
 }
 
-impl<C: fmt::Debug, E: fmt::Debug> fmt::Display for ConfigError<C, E> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            ConfigError::Repository(e) => write!(f, "repository error: {:?}", e),
-            ConfigError::Event(e) => write!(f, "event error: {:?}", e),
-            ConfigError::Validation(errors) => write!(f, "validation errors: {:?}", errors),
-            ConfigError::NotFound => write!(f, "not found"),
-        }
-    }
-}
-
 impl<'a, C, E> ConfigService<'a, C, E>
 where
     C: ConfigRepository,