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/routers/coach_router.py

@@ -1,4 +1,6 @@
-from fastapi import APIRouter, Depends
+from typing import Literal
+
+from fastapi import APIRouter, Depends, Query
 from sqlalchemy.orm import Session
 
 from auth import get_current_user
@@ -12,10 +14,11 @@ router = APIRouter(prefix="/api/coach", tags=["coach"])
 
 @router.get("/session", response_model=CoachSessionResponse)
 def coach_session(
+    track: Literal["accumulation", "book"] = Query("accumulation"),
     db: Session = Depends(get_db),
     current_user: User = Depends(get_current_user),
 ):
-    return memory_coach_service.start_session(db, current_user)
+    return memory_coach_service.start_session(db, current_user, track=track)
 
 
 @router.post("/turn", response_model=CoachTurnResponse)