fix: responder a partir dos livros com embeddings em português

Usa o modelo multilingual, ignora trechos curtos e o template do Llama 3.2
para a resposta sair em uma frase completa. O chat deixa a API livre durante
a geração, o upload indexa o PDF e os agendamentos não são gravados duas vezes.

backend/app/tasks/celery_tasks.py

@@ -30,25 +30,47 @@ def save_schedules(schedules: List[Dict]):
     with open("/app/schedules.json", "w") as f:
         json.dump(schedules, f, indent=2)
 
+def schedule_is_due(schedule: Dict) -> bool:
+    raw = str(schedule.get("time", "")).replace("Z", "+00:00")
+    when = datetime.fromisoformat(raw)
+    if when.tzinfo is not None:
+        when = when.astimezone().replace(tzinfo=None)
+    return datetime.now() >= when
+
+
 @celery.task
 def send_scheduled_message(schedule_id: int = None):
-    """Send one schedule, or every enabled schedule when id is omitted."""
+    """Send enabled schedules whose time has arrived and that were not sent yet."""
     schedules = load_schedules()
-    if schedule_id is None:
-        selected = [item for item in schedules if item.get("enabled", True)]
-    else:
-        selected = [item for item in schedules if item.get("id") == schedule_id and item.get("enabled", True)]
+    due = []
+    for item in schedules:
+        if schedule_id is not None and item.get("id") != schedule_id:
+            continue
+        if not item.get("enabled", True) or item.get("sent"):
+            continue
+        try:
+            ready = schedule_is_due(item)
+        except ValueError:
+            print(f"Invalid schedule time: {item.get('time')}")
+            continue
+        if ready:
+            due.append(item)
 
-    if not selected:
-        print(f"Schedule {schedule_id} not found")
+    if not due:
+        print("No schedules due")
         return
 
-    for schedule in selected:
+    changed = False
+    for schedule in due:
         try:
             bot_service.send_scheduled_message(schedule)
+            schedule["sent"] = True
+            changed = True
             print(f"Sent scheduled message: {schedule['time']}")
         except Exception as e:
             print(f"Error sending scheduled message: {e}")
+    if changed:
+        save_schedules(schedules)
 
 @celery.task
 def generate_daily_content():