fix: cmd_generate usa _active_sessions para la sesión correcta

Si hay una sesión activa registrada para el chat, se consulta
directamente por id en lugar de por created_at DESC, evitando
que /generate use la sesión más reciente en vez de la actual.

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

src/bot/bot.py

@@ -305,12 +305,19 @@ async def cmd_generate(update: Update, ctx: ContextTypes.DEFAULT_TYPE):
     db = ResearchDB(db_conn)
 
     try:
-        # Find last session for this chat
-        cursor = await db_conn.execute(
-            """SELECT * FROM research_sessions WHERE telegram_chat_id = ?
-               ORDER BY created_at DESC LIMIT 1""",
-            (chat_id,)
-        )
+        # Usa la sesión activa si existe, si no la más reciente
+        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,)
+            )
         row = await cursor.fetchone()
         if not row:
             await update.message.reply_text("No research sessions found. Start with /research <topic>")