fix: apply pending correctness fixes

Cherry-pick the still-relevant fixes from recent draft PRs without pulling in stale release/docs changes:

- serialize dashboard data loads to avoid concurrent config self-heal writes
- preserve valid per-model default blocks during dashboard model self-heal
- pass structured humanizeError results directly to toast for model import scan failures
- align frontend kernel isLatest with suffix-aware recommended version ordering

Verification:
- node --test tests/*.test.js
- npm run build

src/pages/models.js

@@ -1308,7 +1308,7 @@ async function importClientConfigs(page, state) {
     const result = await api.scanModelClientConfigs()
     candidates = Array.isArray(result?.candidates) ? result.candidates : []
   } catch (e) {
-    toast(`${t('models.importScanFailed')}: ${humanizeError(e)}`, 'error')
+    toast(humanizeError(e, t('models.importScanFailed')), 'error')
     return
   } finally {
     if (btn) { btn.disabled = false; btn.textContent = oldText || t('models.importClientConfigs') }