feat: 투자 소수점 매매 + 카드 할부(installment_months)

- invest_trade.quantity BIGINT→DECIMAL(18,6): 평단·원가·평가/실현손익 계산을 BigDecimal로 전환 (금액은 원단위 정수 유지)
- account_entry.installment_months 추가: 카드 지출 2~24개월 할부 기록(일시불 null), 응답에 포함

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

src/main/resources/mapper/AccountEntryMapper.xml

@@ -15,6 +15,7 @@
         <result property="walletName" column="wallet_name"/>
         <result property="toWalletId" column="to_wallet_id"/>
         <result property="toWalletName" column="to_wallet_name"/>
+        <result property="installmentMonths" column="installment_months"/>
         <result property="createdAt" column="created_at"/>
         <result property="updatedAt" column="updated_at"/>
     </resultMap>
@@ -28,6 +29,7 @@
         e.id, e.member_id, e.entry_date, e.type, e.category, e.amount, e.memo,
         e.wallet_id, w.name AS wallet_name,
         e.to_wallet_id, tw.name AS to_wallet_name,
+        e.installment_months,
         e.created_at, e.updated_at
     </sql>
     <sql id="entryJoins">
@@ -125,15 +127,16 @@
     <insert id="insert" parameterType="com.sb.web.account.domain.AccountEntry"
             useGeneratedKeys="true" keyProperty="id">
         INSERT INTO account_entry (member_id, entry_date, type, category, amount, memo,
-                                   wallet_id, to_wallet_id, created_at, updated_at)
+                                   wallet_id, to_wallet_id, installment_months, created_at, updated_at)
         VALUES (#{memberId}, #{entryDate}, #{type}, #{category}, #{amount}, #{memo},
-                #{walletId}, #{toWalletId}, NOW(), NOW())
+                #{walletId}, #{toWalletId}, #{installmentMonths}, 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}
+            amount = #{amount}, memo = #{memo}, wallet_id = #{walletId}, to_wallet_id = #{toWalletId},
+            installment_months = #{installmentMonths}
         WHERE id = #{id} AND member_id = #{memberId}
     </update>