feat: multilingual glossary templates + inline GlossarySelector rewrite

- Enriched 8 glossary templates with 18,191 translations across 11 languages
  using LLM batch generation + back-translation validation (99.98% confirmed)
- Rewrote GlossarySelector as inline section with template creation
- Fixed sidebar duplicate (single Glossaries link with proOnly flag)
- Added glossaryId reset when sourceLang changes
- Always show GlossarySelector (locked with Pro badge for free users)
- Added source_language flag on glossary cards
- Redirected /dashboard/context to /dashboard/glossaries
- Updated import endpoint to read translations from templates
- Added enrichment script (scripts/enrich_glossary_templates.py)
- Added 6 i18n keys across all 13 locales

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/app/dashboard/DashboardHeader.tsx

@@ -11,7 +11,7 @@ import {
 import { cn } from '@/lib/utils';
 import { useUser } from './useUser';
 import { useLogout } from './useLogout';
-import { getNavItems } from './constants';
+import { baseNavItems } from './constants';
 import { getInitials, translateTier } from './utils';
 import { ThemeToggle } from '@/components/ui/theme-toggle';
 import { useI18n } from '@/lib/i18n';
@@ -23,7 +23,8 @@ export function DashboardHeader() {
   const { logout } = useLogout();
   const { t } = useI18n();
 
-  const navItems = getNavItems(['pro', 'business', 'enterprise'].includes(user?.tier ?? ''));
+  const isPro = ['pro', 'business', 'enterprise'].includes(user?.tier ?? '');
+  const navItems = isPro ? baseNavItems : baseNavItems.filter(item => !item.proOnly);
 
   return (
     <>