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/db/user_repo.py

@@ -0,0 +1,52 @@
+from bot.db.engine import get_db
+
+
+async def get_or_create(
+    telegram_id: int,
+    username: str | None = None,
+    first_name: str | None = None,
+    lang: str = "en",
+) -> dict:
+    db = await get_db()
+    row = await db.execute_fetchall(
+        "SELECT * FROM users WHERE telegram_id = ?", (telegram_id,)
+    )
+    if row:
+        return dict(row[0])
+
+    await db.execute(
+        "INSERT INTO users (telegram_id, username, first_name, lang) VALUES (?, ?, ?, ?)",
+        (telegram_id, username, first_name, lang),
+    )
+    await db.commit()
+    row = await db.execute_fetchall(
+        "SELECT * FROM users WHERE telegram_id = ?", (telegram_id,)
+    )
+    return dict(row[0])
+
+
+async def update_lang(telegram_id: int, lang: str) -> None:
+    db = await get_db()
+    await db.execute("UPDATE users SET lang = ? WHERE telegram_id = ?", (lang, telegram_id))
+    await db.commit()
+
+
+async def increment_free(telegram_id: int) -> int:
+    db = await get_db()
+    await db.execute(
+        "UPDATE users SET free_used = free_used + 1 WHERE telegram_id = ?",
+        (telegram_id,),
+    )
+    await db.commit()
+    row = await db.execute_fetchall(
+        "SELECT free_used FROM users WHERE telegram_id = ?", (telegram_id,)
+    )
+    return row[0][0]
+
+
+async def get_free_used(telegram_id: int) -> int:
+    db = await get_db()
+    row = await db.execute_fetchall(
+        "SELECT free_used FROM users WHERE telegram_id = ?", (telegram_id,)
+    )
+    return row[0][0] if row else 0