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/http-json/Cargo.toml

@@ -7,6 +7,7 @@ edition = "2024"
 domain.workspace = true
 reqwest.workspace = true
 serde_json.workspace = true
+thiserror.workspace = true
 
 [dev-dependencies]
 tokio.workspace = true