refactor: rename platform/ → sdk/ to avoid stdlib conflict

platform/ shadowed Python's stdlib platform module, breaking
aiogram/aiohttp/multidict at import time. Renamed to sdk/ and
updated all imports across core/, tests/, and adapter/telegram/.

tests/core/test_integration.py

@@ -4,7 +4,7 @@ Smoke test: полный цикл через dispatcher + реальные manag
 Имитирует что делает адаптер (Telegram или Matrix) при получении события.
 """
 import pytest
-from platform.mock import MockPlatformClient
+from sdk.mock import MockPlatformClient
 from core.store import InMemoryStore
 from core.chat import ChatManager
 from core.auth import AuthManager