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/application/src/providers/upsert.rs

@@ -5,10 +5,12 @@ use super::commands::UpsertProviderCommand;
 use super::deps::ProviderDeps;
 
 pub async fn execute(deps: &ProviderDeps, cmd: UpsertProviderCommand) -> DomainResult<()> {
+    let config_json = serde_json::to_string(&cmd.config)
+        .map_err(|e| domain::DomainError::ValidationError(format!("Invalid config: {e}")))?;
     let row = ProviderConfigRow::from_persistence(
         cmd.id,
         cmd.provider_type,
-        cmd.config_json,
+        config_json,
         cmd.enabled,
         String::new(),
     );