Add Vocabulary Learning Platform (Phase 1: DB + API + Editor)

Strategic pivot: Studio-v2 becomes a language learning platform.
Compliance guardrail added to CLAUDE.md — no scan/OCR of third-party
content in customer frontend. Upload of OWN materials remains allowed.

Phase 1.1 — vocabulary_db.py: PostgreSQL model for 160k+ words
with english, german, IPA, syllables, examples, images, audio,
difficulty, tags, translations (multilingual). Trigram search index.

Phase 1.2 — vocabulary_api.py: Search, browse, filters, bulk import,
learning unit creation from word selection. Creates QA items with
enhanced fields (IPA, syllables, image, audio) for flashcards.

Phase 1.3 — /vocabulary page: Search bar with POS/difficulty filters,
word cards with audio buttons, unit builder sidebar. Teacher selects
words → creates learning unit → redirects to flashcards.

Sidebar: Added "Woerterbuch" (/vocabulary) and "Lernmodule" (/learn).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend-lehrer/main.py

@@ -48,6 +48,12 @@ ALERTS_AGENT_ENABLED = os.getenv("ALERTS_AGENT_ENABLED", "false").lower() == "tr
 @asynccontextmanager
 async def lifespan(app: FastAPI):
     logger.info("Backend-Lehrer starting up  (DB search_path=lehrer,core,public)")
+    # Initialize vocabulary tables
+    try:
+        from vocabulary_db import init_vocabulary_tables
+        await init_vocabulary_tables()
+    except Exception as e:
+        logger.warning(f"Vocabulary tables init failed (non-critical): {e}")
     yield
     logger.info("Backend-Lehrer shutting down")
 
@@ -109,6 +115,10 @@ app.include_router(learning_units_router, prefix="/api")
 from progress_api import router as progress_router
 app.include_router(progress_router, prefix="/api")
 
+# --- 4c. Vocabulary Catalog ---
+from vocabulary_api import router as vocabulary_router
+app.include_router(vocabulary_router, prefix="/api")
+
 from unit_api import router as unit_router
 app.include_router(unit_router)  # Already has /api/units prefix