Restructure: Move final 16 root files into packages (backend-lehrer)

classroom/ (+2): state_engine_api, state_engine_models
vocabulary/ (2): api, db
worksheets/ (2): api, models
services/  (+6): audio, email, translation, claude_vision, ai_processor, story_generator
api/        (4): school, klausur_proxy, progress, user_language

Only main.py + config.py remain at root. 16 shims added.

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

backend-lehrer/vocabulary/__init__.py

@@ -0,0 +1,33 @@
+# Vocabulary Module
+# vocabulary/api.py  — API router (search, browse, import, translate)
+# vocabulary/db.py   — PostgreSQL storage for vocabulary word catalog
+
+from .api import router
+from .db import (
+    VocabularyWord,
+    get_pool,
+    init_vocabulary_tables,
+    search_words,
+    get_word,
+    browse_words,
+    insert_word,
+    insert_words_bulk,
+    count_words,
+    get_all_tags,
+    get_all_pos,
+)
+
+__all__ = [
+    "router",
+    "VocabularyWord",
+    "get_pool",
+    "init_vocabulary_tables",
+    "search_words",
+    "get_word",
+    "browse_words",
+    "insert_word",
+    "insert_words_bulk",
+    "count_words",
+    "get_all_tags",
+    "get_all_pos",
+]