feat: multilingual glossary UI, translate selector, context fusion

- TermEditor: rewritten with expandable multilingual translation grid
  (13 languages), editorial styling, source/target + translations JSON
- GlossarySelector: new component in translate page config panel,
  fetches user glossaries, shows flag + term count, Pro+LLM only
- useTranslationConfig: added glossaryId state
- useTranslationSubmit: sends glossary_id to backend
- Context page: removed textarea glossary, presets now create API
  glossaries via template import, added link to Glossaries page
- i18n: added 12 keys × 13 locales for glossary/translate/context

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

frontend/src/app/dashboard/translate/page.tsx

@@ -13,6 +13,7 @@ import { useTranslationConfig } from './useTranslationConfig';
 import { useTranslationSubmit } from './useTranslationSubmit';
 import LanguageSelector from './LanguageSelector';
 import { ProviderSelector } from './ProviderSelector';
+import { GlossarySelector } from './GlossarySelector';
 import { useNotification } from '@/components/ui/notification';
 import { useI18n } from '@/lib/i18n';
 import { API_BASE } from '@/lib/config';
@@ -401,6 +402,14 @@ export default function TranslatePage() {
                       isPro={config.isPro}
                     />
 
+                    {config.isPro && config.mode === 'llm' && (
+                      <GlossarySelector
+                        glossaryId={config.glossaryId}
+                        onChange={config.setGlossaryId}
+                        disabled={submit.isSubmitting}
+                      />
+                    )}
+
                     {/* PDF mode selector */}
                     {isPdf && (
                       <div className="space-y-2">