Fix db.py connection handling and test isolation

db.py:
- Add conn.isolation_level = None to get_conn() — fixes row_factory +
  autocommit conflict. row_factory disables implicit transactions,
  so we need explicit autocommit mode.
- Remove all conn.commit() calls (unnecessary with autocommit)

pyproject.toml:
- Move pytest + pytest-asyncio to main dependencies (uv run pytest
  uses ephemeral env with main deps only)

tests/test_db.py:
- Fix test_upsert_user_updates_username to not chain upsert_user()
  calls in assert expressions (test isolation issue)

apps/telegram-bot/pyproject.toml

@@ -6,10 +6,6 @@ requires-python = ">=3.10"
 dependencies = [
     "python-telegram-bot>=21.6",
     "dateparser>=1.2.0",
-]
-
-[project.optional-dependencies]
-dev = [
     "pytest>=8.3.5",
     "pytest-asyncio>=0.25.2",
 ]