feat: 가계부·게시판 백엔드 API 구현

- com.sb.web 패키지로 재구성: account / auth / board / user / admin / common
- 가계부(account): 내역(필터), 계좌·순자산, 예산, 분류, 정기 거래, 투자 포트폴리오
  (종목·매매 이력, 이동평균 평단·실현/평가손익)
- MyBatis + MariaDB + Redis 세션, BCrypt
- 스키마 자동 초기화(db/*.sql, 멱등), 사용자별 데이터 격리(member_id)
- 문서: docs/BACKEND.md, .env.example

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

src/main/resources/mapper/PostMapper.xml

@@ -0,0 +1,80 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
+        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
+<mapper namespace="com.sb.web.board.mapper.PostMapper">
+
+    <sql id="filter">
+        <if test="tag != null and tag != ''">
+            JOIN post_tag pt ON pt.post_id = p.id
+            JOIN tag t ON t.id = pt.tag_id
+        </if>
+        <where>
+            <if test="tag != null and tag != ''">
+                t.name = #{tag}
+            </if>
+            <if test="keyword != null and keyword != ''">
+                <choose>
+                    <when test="searchType == 'content'">
+                        AND p.content LIKE CONCAT('%', #{keyword}, '%')
+                    </when>
+                    <when test="searchType == 'comment'">
+                        AND EXISTS (SELECT 1 FROM comment c
+                                    WHERE c.post_id = p.id
+                                      AND c.content LIKE CONCAT('%', #{keyword}, '%'))
+                    </when>
+                    <otherwise>
+                        AND p.title LIKE CONCAT('%', #{keyword}, '%')
+                    </otherwise>
+                </choose>
+            </if>
+        </where>
+    </sql>
+
+    <select id="findPage" resultType="com.sb.web.board.dto.PostSummary">
+        SELECT
+            p.id, p.title, p.author_name, p.view_count, p.blocked, p.created_at,
+            (SELECT COUNT(*) FROM comment c WHERE c.post_id = p.id) AS comment_count
+        FROM post p
+        <include refid="filter"/>
+        ORDER BY p.id DESC
+        LIMIT #{size} OFFSET #{offset}
+    </select>
+
+    <select id="countPage" resultType="long">
+        SELECT COUNT(*)
+        FROM post p
+        <include refid="filter"/>
+    </select>
+
+    <select id="findById" parameterType="long" resultType="com.sb.web.board.domain.Post">
+        SELECT id, title, content, author_id, author_name, view_count,
+               blocked, block_reason, created_at, updated_at
+        FROM post
+        WHERE id = #{id}
+    </select>
+
+    <insert id="insert" parameterType="com.sb.web.board.domain.Post"
+            useGeneratedKeys="true" keyProperty="id">
+        INSERT INTO post (title, content, author_id, author_name, view_count, created_at, updated_at)
+        VALUES (#{title}, #{content}, #{authorId}, #{authorName}, 0, NOW(), NOW())
+    </insert>
+
+    <update id="update" parameterType="com.sb.web.board.domain.Post">
+        UPDATE post
+        SET title = #{title}, content = #{content}
+        WHERE id = #{id}
+    </update>
+
+    <delete id="delete" parameterType="long">
+        DELETE FROM post WHERE id = #{id}
+    </delete>
+
+    <update id="increaseViewCount" parameterType="long">
+        UPDATE post SET view_count = view_count + 1 WHERE id = #{id}
+    </update>
+
+    <update id="updateBlocked">
+        UPDATE post SET blocked = #{blocked}, block_reason = #{blockReason} WHERE id = #{id}
+    </update>
+
+</mapper>