Fix NFO 503 error on server reload with config fallback

- Add dynamic config loading in get_nfo_service() dependency
- Handle settings reset during uvicorn reload in development
- Add comprehensive tests for settings priority and fallback behavior
- All 4 unit tests passing (settings priority, config fallback, error cases)
- Update documentation with reload scenario fix

tests/unit/test_nfo_dependency.py

@@ -0,0 +1,112 @@
+"""Tests for NFO service dependency with config fallback.
+
+Tests that get_nfo_service() correctly loads TMDB API key from config.json
+when it's not in settings (e.g., after server reload in development).
+"""
+import pytest
+from unittest.mock import MagicMock, patch
+from fastapi import HTTPException
+
+from src.server.api.nfo import get_nfo_service
+from src.server.models.config import NFOConfig, AppConfig
+from src.config.settings import settings
+
+
+@pytest.mark.asyncio
+async def test_get_nfo_service_with_settings_tmdb_key():
+    """Test get_nfo_service when TMDB key is in settings."""
+    # Set TMDB API key in settings
+    original_key = settings.tmdb_api_key
+    settings.tmdb_api_key = "test_api_key_from_settings"
+    
+    try:
+        nfo_service = await get_nfo_service()
+        assert nfo_service is not None
+        assert nfo_service.tmdb_client.api_key == "test_api_key_from_settings"
+    finally:
+        settings.tmdb_api_key = original_key
+
+
+@pytest.mark.asyncio
+async def test_get_nfo_service_fallback_to_config():
+    """Test get_nfo_service falls back to config.json when key not in settings."""
+    # Clear TMDB API key from settings
+    original_key = settings.tmdb_api_key
+    settings.tmdb_api_key = None
+    
+    try:
+        # Mock config service to return NFO config with API key
+        mock_config = AppConfig(
+            name="Test",
+            data_dir="data",
+            nfo=NFOConfig(
+                tmdb_api_key="test_api_key_from_config",
+                auto_create=False,
+                update_on_scan=False
+            )
+        )
+        
+        with patch('src.server.services.config_service.get_config_service') as mock_get_config:
+            mock_config_service = MagicMock()
+            mock_config_service.load_config.return_value = mock_config
+            mock_get_config.return_value = mock_config_service
+            
+            nfo_service = await get_nfo_service()
+            assert nfo_service is not None
+            assert nfo_service.tmdb_client.api_key == "test_api_key_from_config"
+    finally:
+        settings.tmdb_api_key = original_key
+
+
+@pytest.mark.asyncio
+async def test_get_nfo_service_no_key_raises_503():
+    """Test get_nfo_service raises 503 when no TMDB key available."""
+    # Clear TMDB API key from settings
+    original_key = settings.tmdb_api_key
+    settings.tmdb_api_key = None
+    
+    try:
+        # Mock config service to return config without API key
+        mock_config = AppConfig(
+            name="Test",
+            data_dir="data",
+            nfo=NFOConfig(
+                tmdb_api_key=None,
+                auto_create=False,
+                update_on_scan=False
+            )
+        )
+        
+        with patch('src.server.services.config_service.get_config_service') as mock_get_config:
+            mock_config_service = MagicMock()
+            mock_config_service.load_config.return_value = mock_config
+            mock_get_config.return_value = mock_config_service
+            
+            with pytest.raises(HTTPException) as exc_info:
+                await get_nfo_service()
+            
+            assert exc_info.value.status_code == 503
+            assert "TMDB API key required" in exc_info.value.detail
+    finally:
+        settings.tmdb_api_key = original_key
+
+
+@pytest.mark.asyncio
+async def test_get_nfo_service_config_load_fails_raises_503():
+    """Test get_nfo_service raises 503 when config loading fails."""
+    # Clear TMDB API key from settings
+    original_key = settings.tmdb_api_key
+    settings.tmdb_api_key = None
+    
+    try:
+        # Mock config service to raise exception
+        with patch('src.server.services.config_service.get_config_service') as mock_get_config:
+            mock_get_config.side_effect = Exception("Config file not found")
+            
+            with pytest.raises(HTTPException) as exc_info:
+                await get_nfo_service()
+            
+            assert exc_info.value.status_code == 503
+            assert "TMDB API key required" in exc_info.value.detail
+    finally:
+        settings.tmdb_api_key = original_key