feat: implement adapter/telegram/ with aiogram 3.x

Virtual DM chats, FSM (idle/waiting_response/settings states),
SQLite local DB for tg_users+chats, converter, keyboards, and
handlers for /start, /new, /chats, /settings, confirm callbacks.

adapter/telegram/handlers/auth.py

@@ -0,0 +1,67 @@
+# adapter/telegram/handlers/auth.py
+from __future__ import annotations
+
+from aiogram import Router
+from aiogram.filters import CommandStart
+from aiogram.fsm.context import FSMContext
+from aiogram.types import Message
+
+from adapter.telegram import db
+from adapter.telegram.states import ChatState
+from core.handler import EventDispatcher
+from core.protocol import IncomingCommand
+
+router = Router(name="auth")
+
+
+@router.message(CommandStart())
+async def cmd_start(
+    message: Message,
+    state: FSMContext,
+    dispatcher: EventDispatcher,
+) -> None:
+    tg_id = message.from_user.id
+    display_name = message.from_user.full_name
+
+    # Ensure user exists in platform (mock)
+    from platform.mock import MockPlatformClient
+    # platform is available via dispatcher._platform
+    platform = dispatcher._platform
+    user = await platform.get_or_create_user(
+        external_id=str(tg_id),
+        platform="telegram",
+        display_name=display_name,
+    )
+    platform_user_id = user.user_id
+
+    # Upsert in local DB
+    db.get_or_create_tg_user(tg_id, platform_user_id, display_name)
+
+    last_chat = db.get_last_chat(tg_id)
+
+    if last_chat is None:
+        # New user — create first chat
+        chat_name = "Чат #1"
+        chat_id = db.create_chat(tg_id, chat_name)
+        await state.update_data(active_chat_id=chat_id, active_chat_name=chat_name)
+        await state.set_state(ChatState.idle)
+        await message.answer(
+            f"Привет, {message.from_user.first_name}! 👋\n"
+            f"Я создал тебе первый чат. Просто пиши.\n\n"
+            f"Команды: /new — новый чат, /chats — список чатов"
+        )
+    else:
+        chat_id = last_chat["chat_id"]
+        chat_name = last_chat["name"]
+        await state.update_data(active_chat_id=chat_id, active_chat_name=chat_name)
+        await state.set_state(ChatState.idle)
+        await message.answer(f"С возвращением! Продолжаем [{chat_name}]")
+
+    # Register auth in core
+    event = IncomingCommand(
+        user_id=platform_user_id,
+        platform="telegram",
+        chat_id=chat_id,
+        command="start",
+    )
+    await dispatcher.dispatch(event)