feat: 외화 결제 입력 — 통화+환율→원화 환산, 원본 보존 + 환율 API

- account_entry에 currency/original_amount/exchange_rate 컬럼 추가(멱등 ALTER)
  amount는 환산 원화(표준값) 유지 → 통계·예산 무변경
- AccountEntry/Request/Response·매퍼·서비스에 외화 필드 전달
- FxService(open.er-api.com 무료·무인증, 통화별 일자 캐시) + FxController
  GET /api/fx/rate?from=USD&to=KRW → { from, to, rate }
- WebConfig: /api/fx/** 인증 보호
- (.gitignore: 로컬 시드 스크립트 제외 규칙)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main/resources/mapper/AccountEntryMapper.xml

@@ -18,6 +18,9 @@
         <result property="installmentMonths" column="installment_months"/>
         <result property="pending" column="pending"/>
         <result property="notifKey" column="notif_key"/>
+        <result property="currency" column="currency"/>
+        <result property="originalAmount" column="original_amount"/>
+        <result property="exchangeRate" column="exchange_rate"/>
         <result property="createdAt" column="created_at"/>
         <result property="updatedAt" column="updated_at"/>
     </resultMap>
@@ -32,6 +35,7 @@
         e.wallet_id, w.name AS wallet_name,
         e.to_wallet_id, tw.name AS to_wallet_name,
         e.installment_months, e.pending, e.notif_key,
+        e.currency, e.original_amount, e.exchange_rate,
         e.created_at, e.updated_at
     </sql>
     <sql id="entryJoins">
@@ -141,17 +145,20 @@
             useGeneratedKeys="true" keyProperty="id">
         INSERT INTO account_entry (member_id, entry_date, type, category, amount, memo,
                                    wallet_id, to_wallet_id, installment_months, pending, notif_key,
+                                   currency, original_amount, exchange_rate,
                                    created_at, updated_at)
         VALUES (#{memberId}, #{entryDate}, #{type}, #{category}, #{amount}, #{memo},
                 #{walletId}, #{toWalletId}, #{installmentMonths},
-                COALESCE(#{pending}, 0), #{notifKey}, NOW(), NOW())
+                COALESCE(#{pending}, 0), #{notifKey},
+                #{currency}, #{originalAmount}, #{exchangeRate}, NOW(), NOW())
     </insert>
 
     <update id="update" parameterType="com.sb.web.account.domain.AccountEntry">
         UPDATE account_entry
         SET entry_date = #{entryDate}, type = #{type}, category = #{category},
             amount = #{amount}, memo = #{memo}, wallet_id = #{walletId}, to_wallet_id = #{toWalletId},
-            installment_months = #{installmentMonths}
+            installment_months = #{installmentMonths},
+            currency = #{currency}, original_amount = #{originalAmount}, exchange_rate = #{exchangeRate}
         WHERE id = #{id} AND member_id = #{memberId}
     </update>