Codex 用ファイル追加 (#346) (#347)

#346

Co-authored-by: miteruzo <miteruzo@naver.com>
Reviewed-on: #347

docs/release-checklist.md

@@ -0,0 +1,8 @@
+# Release checklist
+
+- [ ] Backend specs pass
+- [ ] Frontend build passes
+- [ ] No pending migrations
+- [ ] Preview API SSRF checked
+- [ ] BAN behavior checked
+- [ ] CSP checked