test: add unit tests for Telegram bot (HMAC, retry recursion, /start flows)

[Alqku]

Summary

Adds quantara/web_app/tests/test_telegram.py covering the Telegram bot's critical logic (HMAC initData verification, retry recursion on TelegramRetryAfter, both /start flows, plus the except Exception branch in send_health_ratio_notification). Uses deterministic mocking of aiogram Bot calls so the suite is hermetic and CI-friendly.

Changes

• tests/test_telegram.py covers six scenarios for utils.check_telegram_authorization, five scenarios for notifications.send_health_ratio_notification (including the non-retry exception path), and both the basic and deep-link /start flows from handlers/command.py.
• autouse=True fixture snapshots and restores notifications.bot to prevent cross-test pollution.
• Tighter assertion on the formatted HEALTH_RATIO_WARNING_MESSAGE so future refactors that drop the warning template are caught.

Testing

• python -m py_compile clean on the new test file.
• pytest-asyncio is configured with asyncio_mode = "strict" in quantara/pyproject.toml so every async test method is explicitly marked.
• Mocks at the bot.send_message boundary; no network calls or bot token required.

Closes #62

[Alqku]

@github-actions re-run ci