fix: cmd_publish usa _active_sessions para la sesión correcta

Mismo patrón que cmd_generate: si hay sesión activa registrada
para el chat, consulta por id; si no, fallback a created_at DESC.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/bot/bot.py

@@ -963,6 +963,13 @@ async def cmd_publish(update: Update, ctx: ContextTypes.DEFAULT_TYPE):
             )
             return
 
+        session_id = _active_sessions.get(chat_id)
+        if session_id:
+            cursor = await db_conn.execute(
+                "SELECT * FROM research_sessions WHERE id = ?",
+                (session_id,)
+            )
+        else:
             cursor = await db_conn.execute(
                 "SELECT * FROM research_sessions WHERE telegram_chat_id = ? ORDER BY created_at DESC LIMIT 1",
                 (chat_id,)