Add multi-user features: i18n, payments, multi-model AI, focus areas

Replace single report type with composable analysis: depth levels
(basic/standard/full) + focus area multi-select (psychology, business,
marketing, content, audience, sentiment). Multi-step inline keyboard
flow guides users through selection.

- i18n: English + Russian, auto-detect from Telegram, /lang override
- AI providers: Anthropic + OpenRouter via AIClient abstraction
- Telegram Stars payments with per-depth pricing and free trial
- SQLite (aiosqlite) for users, analyses, payments tracking
- User middleware for auto-registration and language detection
- Report persistence: save .md locally, offer file download
- New commands: /features, /prices, /lang
- Composable prompt system: depth modifiers + focus area fragments

bot/middleware/user_middleware.py

@@ -0,0 +1,41 @@
+from typing import Any, Awaitable, Callable
+
+from aiogram import BaseMiddleware
+from aiogram.types import TelegramObject, Update
+
+from bot.db import user_repo
+from bot.i18n import Lang, detect_lang
+
+
+class UserMiddleware(BaseMiddleware):
+    async def __call__(
+        self,
+        handler: Callable[[TelegramObject, dict[str, Any]], Awaitable[Any]],
+        event: TelegramObject,
+        data: dict[str, Any],
+    ) -> Any:
+        user = None
+        if isinstance(event, Update):
+            if event.message and event.message.from_user:
+                user = event.message.from_user
+            elif event.callback_query and event.callback_query.from_user:
+                user = event.callback_query.from_user
+            elif event.pre_checkout_query and event.pre_checkout_query.from_user:
+                user = event.pre_checkout_query.from_user
+        elif hasattr(event, "from_user") and event.from_user:
+            user = event.from_user
+
+        if user:
+            db_user = await user_repo.get_or_create(
+                telegram_id=user.id,
+                username=user.username,
+                first_name=user.first_name,
+                lang=detect_lang(user.language_code).value,
+            )
+            data["lang"] = Lang(db_user["lang"])
+            data["db_user"] = db_user
+        else:
+            data["lang"] = Lang.EN
+            data["db_user"] = None
+
+        return await handler(event, data)