feat: add download target type for fetching files from URLs

tests/test_config.py

@@ -7,7 +7,7 @@ from pathlib import Path
 import pytest
 import yaml
 
-from hokusai.config import load_config
+from hokusai.config import GenerateTargetConfig, load_config
 
 
 class TestLoadConfig:
@@ -21,7 +21,9 @@ class TestLoadConfig:
         config = load_config(config_path)
 
         assert "out.txt" in config.targets
-        assert config.targets["out.txt"].prompt == "hello"
+        target = config.targets["out.txt"]
+        assert isinstance(target, GenerateTargetConfig)
+        assert target.prompt == "hello"
         assert config.defaults.text_model == "pixtral-large-latest"
         assert config.defaults.image_model == "flux-2-pro"
 
@@ -56,6 +58,7 @@ class TestLoadConfig:
         assert config.defaults.image_model == "custom-image"
 
         banner = config.targets["banner.png"]
+        assert isinstance(banner, GenerateTargetConfig)
         assert banner.model == "flux-dev"
         assert banner.width == 1920
         assert banner.height == 480
@@ -63,6 +66,7 @@ class TestLoadConfig:
         assert banner.control_images == ["ctrl.png"]
 
         story = config.targets["story.md"]
+        assert isinstance(story, GenerateTargetConfig)
         assert story.model is None
         assert story.inputs == ["banner.png"]