fix(p3.2): model_version_tracker 改 pure unit test + probe 改善

Engineer 重寫 test_model_version_tracker：
- 用 _make_fake_ctx (asynccontextmanager) 完整 mock get_db_context
- 移除 @pytest.mark.integration（整 class）
- patch probe_all_providers + get_db_context 雙路徑
- 4 testcases 全綠，無真實 PG 依賴

model_version_probe.py 配套改善（match 新 test mock 預期）

Tests: 19 passed (probe 15 + tracker 4)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/api/src/services/model_version_probe.py

@@ -20,6 +20,8 @@ from datetime import datetime, timedelta, timezone
 
 import structlog
 
+from src.core.config import settings
+
 logger = structlog.get_logger(__name__)
 
 TAIPEI_TZ = timezone(timedelta(hours=8))
@@ -91,8 +93,6 @@ async def probe_gemini_version() -> ProviderVersionInfo:
     Raises:
         RuntimeError: GEMINI_API_KEY 未設定
     """
-    from src.core.config import settings
-
     api_key = settings.GEMINI_API_KEY
     if not api_key:
         raise RuntimeError("GEMINI_API_KEY not configured")
@@ -147,8 +147,6 @@ async def probe_claude_version() -> ProviderVersionInfo:
     Raises:
         RuntimeError: CLAUDE_API_KEY 未設定
     """
-    from src.core.config import settings
-
     api_key = settings.CLAUDE_API_KEY
     if not api_key:
         raise RuntimeError("CLAUDE_API_KEY not configured")
@@ -182,8 +180,6 @@ async def probe_openclaw_nemo_version() -> ProviderVersionInfo:
         RuntimeError: OPENCLAW_DEFAULT_MODEL 未設定
         httpx.HTTPError: 連線失敗
     """
-    from src.core.config import settings
-
     model = settings.OPENCLAW_DEFAULT_MODEL
     if not model:
         raise RuntimeError("OPENCLAW_DEFAULT_MODEL not configured")
@@ -238,8 +234,6 @@ async def probe_all_providers() -> list[ProviderVersionInfo]:
         - 使用 return_exceptions=True 確保任一 provider 失敗不影響其他
         - 每個 exception 都有對應的 log warning
     """
-    from src.core.config import settings
-
     tasks = [
         probe_ollama_version(settings.OLLAMA_URL, settings.OLLAMA_HEALTH_CHECK_MODEL),
         probe_ollama_version(