fix(presentation): extract 12 handler violations to use cases

- TokenService port + JwtTokenService adapter; login/refresh return LoginResult
- delete get_token (dup of login); create_tokens helper removed
- type UpdateChannelRequest schedule_config/recycle_policy (no serde_json::Value)
- update_settings returns updated Vec; handler calls one use case
- config use case in application::config; handler maps DTO only
- SyncStatusEntry moved to api-types w/ From<LibrarySyncLogEntry>
- trigger_sync: Conflict error, drop sync_trigger.send from handler
- UpsertProviderCommand.config accepts Value; serialization in use case
- get_current_broadcast returns BroadcastWithChannel; one call
- get_stream_url resolves broadcast internally; handler single call

crates/presentation/src/handlers/providers.rs

@@ -43,13 +43,10 @@ pub async fn upsert_provider(
     Path(id): Path<String>,
     Json(req): Json<ProviderConfigRequest>,
 ) -> Result<Json<serde_json::Value>, AppError> {
-    let config_json = serde_json::to_string(&req.config)
-        .map_err(|e| AppError(DomainError::ValidationError(format!("Invalid config JSON: {e}"))))?;
-
     let cmd = UpsertProviderCommand {
         id,
         provider_type: req.provider_type,
-        config_json,
+        config: req.config,
         enabled: req.enabled,
     };
     application::providers::upsert::execute(&state.provider_deps, cmd).await?;