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

locales/zh-TW.json

@@ -1292,12 +1292,15 @@
                     "earlyAccess": "搶先體驗",
                     "earlyAccessTooltip": "此版本目前需要 Civitai 搶先體驗權限",
                     "ignored": "已忽略",
-                    "ignoredTooltip": "此版本已關閉更新通知"
+                    "ignoredTooltip": "此版本已關閉更新通知",
+                    "onSiteOnly": "僅站內生成",
+                    "onSiteOnlyTooltip": "此版本僅在 Civitai 站內可用，無法下載"
                 },
                 "actions": {
                     "download": "下載",
                     "downloadTooltip": "下載此版本",
                     "downloadEarlyAccessTooltip": "從 Civitai 下載此搶先體驗版本",
+                    "downloadNotAllowedTooltip": "此版本僅在 Civitai 站內可用，無法下載",
                     "delete": "刪除",
                     "deleteTooltip": "刪除此本地版本",
                     "ignore": "忽略",