fix(08): apply code review findings (CR-01, CR-02, WR-01–05, IN-01)

- CR-01: fix SSRF bypass — isPrivateIpv6 now delegates ::ffff:<ipv4> to
  isPrivateIpv4, covering 172.16-31.x and 169.254.x ranges
- CR-02: add ParseUUIDPipe to GET /favorites widgetId param + service guard
  so missing widgetId returns 400 instead of leaking all user favorites
- WR-01: link-widget — replace raw 'link.error' key with t('link.error') (4 sites)
- WR-02: favorites-widget — fix load-path error to use t('favorites.error')
- WR-03: widget-catalog-modal — move aria-hidden from outer wrapper to backdrop
- WR-04: calculator — remove duplicate M button (MR clone); MC/MR/M+/M−/MS remain
- WR-05: schema — add FavoriteLink→WidgetInstance FK with onDelete:Cascade
- IN-01: create-widget.dto.ts — update comment from four to eight supported types

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/src/components/dashboard/widgets/favorites-widget.tsx

@@ -70,8 +70,7 @@ export function FavoritesWidget({
         const data = await fetchFavorites(instanceId);
         if (!cancelled) setFavorites(data);
       } catch {
-        // Use a stable error key — t is excluded from deps intentionally
-        if (!cancelled) setError('favorites.error');
+        if (!cancelled) setError(t('favorites.error'));
       } finally {
         if (!cancelled) setLoading(false);
       }