feat: 순자산 추이 주간 집계 추가 (/networth/trend?unit=WEEK)

- weeklyWalletFlow(월요일 기준 주별 순현금흐름) + netWorthTrendWeekly(기본 13주)
- 컨트롤러에 unit=WEEK&weeks=N 지원(기존 월별은 그대로)

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

src/main/resources/mapper/AccountEntryMapper.xml

@@ -108,6 +108,17 @@
         ORDER BY ym
     </select>
 
+    <select id="weeklyWalletFlow" resultType="map">
+        SELECT DATE_FORMAT(DATE_SUB(entry_date, INTERVAL WEEKDAY(entry_date) DAY), '%Y-%m-%d') AS wk,
+               COALESCE(SUM(CASE WHEN type = 'INCOME' THEN amount
+                                 WHEN type = 'EXPENSE' THEN -amount
+                                 ELSE 0 END), 0) AS net
+        FROM account_entry
+        WHERE member_id = #{memberId} AND wallet_id IS NOT NULL AND type IN ('INCOME', 'EXPENSE')
+        GROUP BY wk
+        ORDER BY wk
+    </select>
+
     <select id="statsByPeriod" resultType="map">
         SELECT
         <choose>