fix(tg): reviewer fixes — error handling, timeouts, db index

- commands.py: try/except TelegramBadRequest around all Bot API calls (#2);
  /new handles "topics limit" with user-friendly message (#4)
- start.py: isolate _check_and_prune_stale_topics with try/except Exception (#3)
- message.py: asyncio.timeout(30) around stream_message; handle TimeoutError (#6)
- db.py: add idx_chats_user_id index in init_db() (#7)
- settings.py: remove dead active_chat_id variable (#8)
- tests: add test_message.py (stream error/success); add 2 tests in test_commands.py
  (topics limit, /archive in General topic)

tests/adapter/telegram/test_commands.py

@@ -5,6 +5,7 @@ from types import SimpleNamespace
 from unittest.mock import AsyncMock, MagicMock
 
 import pytest
+from aiogram.exceptions import TelegramBadRequest
 
 
 @pytest.fixture(autouse=True)
@@ -74,3 +75,28 @@ async def test_cmd_rename_updates_db_and_topic(fresh_db, monkeypatch):
         chat_id=100, message_thread_id=42, name="Работа"
     )
     assert fresh_db.get_chat(1, 42)["chat_name"] == "Работа"
+
+
+async def test_cmd_new_topics_limit(fresh_db):
+    """When Telegram returns topics limit error, user gets a friendly message."""
+    import adapter.telegram.handlers.commands as mod
+    importlib.reload(mod)
+    msg = make_message(user_id=1, thread_id=42, chat_id=100)
+    msg.bot.create_forum_topic = AsyncMock(
+        side_effect=TelegramBadRequest(method=MagicMock(), message="topics limit exceeded")
+    )
+    await mod.cmd_new(msg)
+    msg.answer.assert_called_once()
+    assert "лимит" in msg.answer.call_args[0][0]
+    # No chat should be created
+    assert fresh_db.count_active_chats(1) == 0
+
+
+async def test_cmd_archive_general_topic(fresh_db):
+    """/archive in General topic (thread_id=None) replies with 'not found'."""
+    import adapter.telegram.handlers.commands as mod
+    importlib.reload(mod)
+    msg = make_message(user_id=1, thread_id=None, chat_id=100)
+    await mod.cmd_archive(msg)
+    msg.answer.assert_called_once()
+    msg.bot.close_forum_topic.assert_not_called()