cleanup: drop redundant @pytest.mark.asyncio + fix log_id type

- pyproject already sets asyncio_mode=auto, so async def tests are
  collected as async automatically. Removed the redundant decorator
  from four files (test_i18n, test_llm_csv_parser, test_ticker_validate,
  test_localization_integration); the bare async def is enough.
- StrategicLogTranslation.log_id used the _PK autoincrement type for
  a non-PK FK column. Replaced with a portable BigInteger that emits
  Integer on SQLite and BigInteger elsewhere — matches the migration's
  sa.BigInteger() declaration.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/test_i18n.py

@@ -44,7 +44,6 @@ def test_respond_in_clause_unknown_lang_falls_back_to_english():
     assert respond_in_clause("xx") == ""
 
 
-@pytest.mark.asyncio
 async def test_translate_happy_path(monkeypatch):
     from unittest.mock import AsyncMock, MagicMock
 
@@ -66,7 +65,6 @@ async def test_translate_happy_path(monkeypatch):
     assert llm_log.cost_usd == pytest.approx(0.00002)
 
 
-@pytest.mark.asyncio
 async def test_translate_strips_code_fences(monkeypatch):
     """If the LLM wraps the output in ```markdown ... ```, strip it."""
     from unittest.mock import AsyncMock, MagicMock
@@ -85,7 +83,6 @@ async def test_translate_strips_code_fences(monkeypatch):
     assert translated.startswith("# Titolo")
 
 
-@pytest.mark.asyncio
 async def test_translate_provider_failure_propagates(monkeypatch):
     from unittest.mock import AsyncMock, MagicMock
 
@@ -98,7 +95,6 @@ async def test_translate_provider_failure_propagates(monkeypatch):
         await mod.translate(client, "# Title\n\nBody.", "it")
 
 
-@pytest.mark.asyncio
 async def test_translate_unknown_lang_returns_source_unchanged(monkeypatch):
     """Defensive: an unknown lang code (or 'en') short-circuits without
     calling the LLM. Callers shouldn't have to gate the call themselves."""