fix(s09_memory): point read/write arrow at memory files box

Make the Storage to Memory Files arrow a straight vertical segment
ending at the box edge, instead of curving onto the dashed border.
Applies to the en, ja, and zh (default) diagram variants.

s09_memory/images/memory-subsystems.en.svg

@@ -53,7 +53,7 @@
   <text x="370" y="203" fill="#475569" font-size="11" text-anchor="middle">.memory/ — MEMORY.md index + *.md files (YAML frontmatter: name / description / type)</text>
 
   <!-- Arrow: Storage → Memory Files -->
-  <path d="M 112 138 L 112 174 Q 112 180 118 180" fill="none" stroke="#7c3aed" stroke-width="1.5" marker-end="url(#arrow)"/>
+  <path d="M 112 138 L 112 180" fill="none" stroke="#7c3aed" stroke-width="1.5" marker-end="url(#arrow)"/>
   <text x="120" y="162" fill="#7c3aed" font-size="9">read/write</text>
 
   <!-- Arrow: Extraction → Memory Files -->

s09_memory/images/memory-subsystems.ja.svg

@@ -53,7 +53,7 @@
   <text x="370" y="203" fill="#475569" font-size="11" text-anchor="middle">.memory/ — MEMORY.md インデックス + *.md ファイル（YAML frontmatter: name / description / type）</text>
 
   <!-- Arrow: ストレージ → Memory Files -->
-  <path d="M 112 138 L 112 174 Q 112 180 118 180" fill="none" stroke="#7c3aed" stroke-width="1.5" marker-end="url(#arrow)"/>
+  <path d="M 112 138 L 112 180" fill="none" stroke="#7c3aed" stroke-width="1.5" marker-end="url(#arrow)"/>
   <text x="120" y="162" fill="#7c3aed" font-size="9">読み/書き</text>
 
   <!-- Arrow: 抽出 → Memory Files -->

s09_memory/images/memory-subsystems.svg

@@ -53,7 +53,7 @@
   <text x="370" y="203" fill="#475569" font-size="11" text-anchor="middle">.memory/ — MEMORY.md 索引 + *.md 文件（YAML frontmatter: name / description / type）</text>
 
   <!-- Arrow: 存储 → Memory Files -->
-  <path d="M 112 138 L 112 174 Q 112 180 118 180" fill="none" stroke="#7c3aed" stroke-width="1.5" marker-end="url(#arrow)"/>
+  <path d="M 112 138 L 112 180" fill="none" stroke="#7c3aed" stroke-width="1.5" marker-end="url(#arrow)"/>
   <text x="120" y="162" fill="#7c3aed" font-size="9">写入/读取</text>
 
   <!-- Arrow: Extraction → Memory Files -->