Add German IPA support (wiki-pronunciation-dict + epitran)

Hybrid approach mirroring English IPA:
- Primary: wiki-pronunciation-dict (636k entries, CC-BY-SA, Wiktionary)
- Fallback: epitran rule-based G2P (MIT license)

IPA modes now use language-appropriate dictionaries:
- auto/en: English IPA (Britfone + eng_to_ipa)
- de: German IPA (wiki-pronunciation-dict + epitran)
- all: EN column gets English IPA, other columns get German IPA
- none: disabled

Frontend shows CC-BY-SA attribution when German IPA is active.

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

admin-lehrer/components/grid-editor/useGridEditor.ts

@@ -14,7 +14,7 @@ export interface GridEditorState {
   selectedZone: number | null
 }
 
-export type IpaMode = 'auto' | 'all' | 'en' | 'none'
+export type IpaMode = 'auto' | 'all' | 'de' | 'en' | 'none'
 export type SyllableMode = 'auto' | 'all' | 'de' | 'en' | 'none'
 
 export function useGridEditor(sessionId: string | null) {