debug: 添加静态文件路径调试日志，排查空白页面问题

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

api/server.py

@@ -103,17 +103,32 @@ app.include_router(courseware_router)
 # ----------------------------
 # Static hosting (Vite build)
 # ----------------------------
+print(f"[DEBUG] WEB_DIST: {WEB_DIST}")
+print(f"[DEBUG] WEB_INDEX: {WEB_INDEX}")
+print(f"[DEBUG] WEB_ASSETS: {WEB_ASSETS}")
+print(f"[DEBUG] WEB_INDEX exists: {os.path.exists(WEB_INDEX)}")
+print(f"[DEBUG] WEB_ASSETS exists: {os.path.isdir(WEB_ASSETS)}")
+print(f"[DEBUG] WEB_DIST exists: {os.path.isdir(WEB_DIST)}")
+
 if os.path.isdir(WEB_ASSETS):
+    print(f"[DEBUG] Mounting /assets from {WEB_ASSETS}")
     app.mount("/assets", StaticFiles(directory=WEB_ASSETS), name="assets")
+else:
+    print(f"[WARNING] WEB_ASSETS directory not found: {WEB_ASSETS}")
 
 if os.path.isdir(WEB_DIST):
+    print(f"[DEBUG] Mounting /static from {WEB_DIST}")
     app.mount("/static", StaticFiles(directory=WEB_DIST), name="static")
+else:
+    print(f"[WARNING] WEB_DIST directory not found: {WEB_DIST}")
 
 
 @app.get("/")
 def index():
     if os.path.exists(WEB_INDEX):
+        print(f"[DEBUG] Serving index.html from {WEB_INDEX}")
         return FileResponse(WEB_INDEX)
+    print(f"[ERROR] WEB_INDEX not found: {WEB_INDEX}")
     return JSONResponse(
         {"detail": "web/build not found. Build frontend first (web/build/index.html)."},
         status_code=500,