feat: add license information handling for Civitai models

Add license resolution utilities and integrate license information into model metadata processing. The changes include:

- Add `resolve_license_payload` function to extract license data from Civitai model responses
- Integrate license information into model metadata in CivitaiClient and MetadataSyncService
- Add license flags support in model scanning and caching
- Implement CommercialUseLevel enum for standardized license classification
- Update model scanner to handle unknown fields when extracting metadata values

This ensures proper license attribution and compliance when working with Civitai models.

tests/utils/test_civitai_utils.py

@@ -0,0 +1,35 @@
+from py.utils.civitai_utils import (
+    CommercialUseLevel,
+    build_license_flags,
+    resolve_license_info,
+    resolve_license_payload,
+)
+
+
+def test_resolve_license_payload_defaults():
+    payload, flags = resolve_license_info({})
+
+    assert payload["allowNoCredit"] is True
+    assert payload["allowDerivatives"] is True
+    assert payload["allowDifferentLicense"] is True
+    assert payload["allowCommercialUse"] == ["Sell"]
+    assert flags == 57
+
+
+def test_build_license_flags_custom_values():
+    source = {
+        "allowNoCredit": False,
+        "allowCommercialUse": {"Image", "Sell"},
+        "allowDerivatives": False,
+        "allowDifferentLicense": False,
+    }
+
+    payload = resolve_license_payload(source)
+    assert payload["allowNoCredit"] is False
+    assert set(payload["allowCommercialUse"]) == {"Image", "Sell"}
+    assert payload["allowDerivatives"] is False
+    assert payload["allowDifferentLicense"] is False
+
+    flags = build_license_flags(source)
+    # Highest commercial level is SELL -> level 4 -> shifted by 1 == 8.
+    assert flags == (CommercialUseLevel.SELL << 1)