fix context sentences in YAML to ensure vocab emphasis

docs/howtostudykorean/theme/02-transportation.md

@@ -117,7 +117,7 @@ vocabulary:
         [길 tends to emphasize the route/path itself — a road to walk or drive on — while 거리 tends to emphasize the street as a place/area.]
       examples:
         - ko: 저는 **길**을 잃었어요
-          en: I'm lost
+          en: I'm **lost**
         - ko: 우리는 **길**을 건너야 돼요
           en: We have to cross the **street**
         - ko: 이 **길**에서 직진하셔요
@@ -148,9 +148,9 @@ vocabulary:
       examples:
         - ko: "**교통카드**를 어디서 살 수 있어요?"
           en: Where can you buy a **transportation card**?
-        - ko: 교통 카드를 어디서 충전할 수 있어요?
+        - ko: "**교통 카드**를 어디서 충전할 수 있어요?"
           en: Where can I charge my **transportation card**?
-        - ko: 교통 카드를 잃어버렸어요
+        - ko: "**교통 카드**를 잃어버렸어요"
           en: I lost my **transportation card**?
 
     - ko: 자리

docs/howtostudykorean/theme/03-eating.md

@@ -866,9 +866,9 @@ vocabulary:
     - ko: 김밥
       en: A roll of rice and other ingredients wrapped in seaweed
       examples:
-        - ko: 김밥 1줄 주세요
+        - ko: "**김밥** 1줄 주세요"
           en: One (line) of **kimbab** please
-        - ko: 김밥은 얼마예요?
+        - ko: "**김밥**은 얼마예요?"
           en: How much is (the) **kimbab**?
 
     - ko: 떡

docs/howtostudykorean/theme/04-shopping.md

@@ -425,10 +425,10 @@ vocabulary:
       notes: |
         The examples below use the related noun form 환불 (refund) with 되다/받다, which is very common in everyday speech alongside the plain verb 환불하다.
       examples:
-        - ko: "환불은 안 됩니다"
-          en: "No refund"
-        - ko: "사과가 다 상해서 환불을 받아야 돼요"
-          en: "I need to get a refund because all the apples have gone bad"
+        - ko: "**환불**은 안 됩니다"
+          en: "No **refund**"
+        - ko: "사과가 다 상해서 **환불**을 받아야 돼요"
+          en: "I need to get a **refund** because all the apples have gone bad"
 
     - ko: "비교하다"
       en: "to compare"