fix(download): accept newer CivitAI file types for primary file selection

Downloads failed with "No suitable file found in metadata" for models whose
only file uses newer CivitAI file types (e.g. 'Enhancement LoRA' for
Anima/AIR image-editing LoRAs) because the primary-file allowlist only
covered legacy types.

- unify the weights-type allowlist as MODEL_WEIGHT_FILE_TYPES
  (py/utils/constants.py) and apply it across download, recipe and
  metadata-refresh lookups
- mirror CivitAI's getPrimaryFile() semantics: prefer weights-type primary,
  fall back to weights files, then trust CivitAI's primary flag (excluding
  non-downloadable artifacts like Config/Archive/Workflow)
- mirror the allowlist in the frontend via shared isModelWeightFile() helper
- add regression tests for the Enhancement LoRA primary-file download,
  primary-flag fallback and weights-over-non-weights-primary preference

static/js/utils/modelFileTypes.js

@@ -0,0 +1,15 @@
+// CivitAI ModelFile.type values eligible as the main download file.
+// Mirrors the backend constant MODEL_WEIGHT_FILE_TYPES (py/utils/constants.py).
+// Keep both lists in sync when CivitAI introduces new file types.
+export const MODEL_WEIGHT_FILE_TYPES = [
+    'Model',
+    'Pruned Model',
+    'Negative',
+    'UNet',
+    'Diffusion Model',
+    'Enhancement LoRA',
+];
+
+export function isModelWeightFile(type) {
+    return MODEL_WEIGHT_FILE_TYPES.includes(type);
+}