feat(usage-control): add support for Civitai usageControl field

Handle models that are only available for on-site generation (usageControl:
"Generation" or "InternalGeneration") rather than downloadable.

Backend changes:
- Add usage_control field to ModelVersionRecord dataclass
- Extract usageControl from Civitai API responses
- Filter non-downloadable versions from update availability checks
- Add database schema migration for usage_control column
- Include usageControl in version response JSON

Frontend changes:
- Add isDownloadAllowed() helper function
- Show disabled download button for non-downloadable versions
- Add "On-Site Only" badge for restricted versions
- Update resolveUpdateAvailability() to filter non-downloadable versions
- Add CSS styling for disabled action button

Internationalization:
- Add translations for onSiteOnly badge and downloadNotAllowedTooltip
- Complete translations for all 10 supported languages

static/css/components/lora-modal/versions.css

@@ -374,6 +374,14 @@
     background: color-mix(in oklch, var(--lora-surface) 35%, transparent);
 }
 
+.version-action-disabled {
+    background: transparent;
+    border-color: var(--border-color);
+    color: var(--text-muted);
+    opacity: 0.6;
+    cursor: not-allowed;
+}
+
 .version-action:disabled {
     opacity: 0.6;
     cursor: not-allowed;