feat(agent): improve enrich_hf_metadata skill with priority_tags, preview_url fix, civitai.trainedWords

- Add identify_model_type() helper to determine lora/checkpoint/embedding
- Pass priority_tags from user settings to LLM prompt for tag relevance
- SKILL.md: instruct LLM to exclude technical/generic HF tags, cross-reference
  against priority_tags; forbid ['None'] placeholder for trigger words
- post_processor: fix preview_url not updated after download (now writes local
  .webp path to metadata); write trigger words to civitai.trainedWords instead
  of top-level; sanitize ['None']/'null'/'n/a' placeholder values to []
- download_preview() now returns str | None (local path) instead of bool
- Update tests for new return type and nested civitai.trainedWords structure

tests/services/test_post_processor.py

@@ -44,7 +44,7 @@ class TestProcessDispatch:
             mock.patch("py.agent_cli.refresh_cache") as mock_ref,
         ):
             mock_apply.return_value = ["metadata_source"]
-            mock_dl.return_value = False
+            mock_dl.return_value = None
 
             result = await processor.process(
                 skill_name="enrich_hf_metadata",
@@ -155,7 +155,7 @@ class TestEnrichHfMetadata:
         llm = {**self.MIN_LLM_OUTPUT, "trigger_words": ["trigger1", "trigger2"]}
         with (
             mock.patch("py.agent_cli.apply_metadata_updates") as mock_apply,
-            mock.patch("py.agent_cli.download_preview", return_value=False),
+            mock.patch("py.agent_cli.download_preview", return_value=None),
             mock.patch("py.agent_cli.refresh_cache"),
         ):
             await processor.process(
@@ -165,7 +165,7 @@ class TestEnrichHfMetadata:
                 metadata={"trainedWords": []},
             )
         applied = mock_apply.call_args[0][1]
-        assert applied["trainedWords"] == ["trigger1", "trigger2"]
+        assert applied["civitai"]["trainedWords"] == ["trigger1", "trigger2"]
 
     # -- description -----------------------------------------------------
 
@@ -237,7 +237,7 @@ class TestEnrichHfMetadata:
             mock.patch("py.agent_cli.download_preview") as mock_dl,
             mock.patch("py.agent_cli.refresh_cache"),
         ):
-            mock_dl.return_value = True
+            mock_dl.return_value = "/p.webp"
             result = await processor.process(
                 skill_name="enrich_hf_metadata",
                 model_path="/p.safetensors",
@@ -246,6 +246,8 @@ class TestEnrichHfMetadata:
             )
         assert result["preview_downloaded"] is True
         mock_dl.assert_awaited_once_with("/p.safetensors", "https://ex.com/img.png")
+        applied = mock_apply.call_args[0][1]
+        assert applied["preview_url"] == "/p.webp"
 
     @pytest.mark.asyncio
     async def test_preview_skipped_when_exists(self, processor):