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-sqlite/Cargo.toml

@@ -8,6 +8,7 @@ domain.workspace = true
 sqlx.workspace = true
 serde.workspace = true
 serde_json.workspace = true
+thiserror.workspace = true
 
 [dev-dependencies]
 tokio.workspace = true

crates/adapters/config-sqlite/src/error.rs

@@ -1,14 +1,7 @@
-#[derive(Debug)]
+#[derive(Debug, thiserror::Error)]
 pub enum SqliteConfigError {
-    Sql(sqlx::Error),
+    #[error("sql: {0}")]
+    Sql(#[from] sqlx::Error),
+    #[error("serialization: {0}")]
     Serialization(String),
 }
-
-impl std::fmt::Display for SqliteConfigError {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            SqliteConfigError::Sql(e) => write!(f, "sql: {e}"),
-            SqliteConfigError::Serialization(e) => write!(f, "serialization: {e}"),
-        }
-    }
-}