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

py/routes/handlers/model_handlers.py

@@ -2423,6 +2423,7 @@ class ModelUpdateHandler:
             "shouldIgnore": version.should_ignore,
             "earlyAccessEndsAt": version.early_access_ends_at,
             "isEarlyAccess": is_early_access,
+            "usageControl": version.usage_control,
             "filePath": context.get("file_path"),
             "fileName": context.get("file_name"),
         }