Instructions per chat (system prompt addition; UI dialog and Telegram /prompt)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/src/jobs.rs

@@ -164,6 +164,7 @@ pub async fn run_with(app: &Arc<App>, job: &Job, trigger: &str, payload: Option<
         pinned: false,
         archived: false,
         folder: None,
+        instructions: String::new(),
     };
     let session = app.save_session(session)?;
     app.store.job_started(&job.id, &session.id, now)?;