Add word-book practice, iOS app shell, and fix embedded WebView blank screen.

Ship dual-track learning (daily accumulation vs textbook),沪教/商务词书 APIs and UI, native iOS wrapper with bundled H5, and production book import on deploy.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/services/memory_coach_service.py

@@ -216,13 +216,25 @@ class MemoryCoachService:
                 t.revealed = True
         return tokens
 
-    def start_session(self, db: Session, user: User) -> CoachSessionResponse:
-        settings = quiz_service.get_settings(db, user)
-        words = quiz_service.select_daily_words(db, user, settings.daily_target)
+    def start_session(self, db: Session, user: User, track: str = "accumulation") -> CoachSessionResponse:
+        from services.book_service import book_service
+
+        if track == "book":
+            book = book_service.get_active_book(db, user)
+            if not book:
+                return CoachSessionResponse(words=[], total=0)
+            book_service.ensure_user_book_words(db, user, book)
+            practice = book_service.practice_settings_dict(db, user, book)
+            words = quiz_service.select_book_words(db, user, book, practice["daily_target"])
+            book_id = book.id
+        else:
+            settings = quiz_service.get_settings(db, user)
+            words = quiz_service.select_accumulation_words(db, user, settings.daily_target)
+            book_id = 0
         if not words:
             return CoachSessionResponse(words=[], total=0)
 
-        summaries = memory_visual_service.get_visualization(db, user)["words"]
+        summaries = memory_visual_service.get_visualization(db, user, book_id=book_id)["words"]
         risk_map = {w["id"]: w.get("retention_now", 0) for w in summaries}
 
         items = [