v2.2.3: stage updater.exe outside dist/ to survive main.spec --clean

main.spec's --clean flag wipes dist/ at the start of main.exe build,
which deleted dist/updater.exe before it could be embedded as data
(v2.2.2 main.exe shipped without embedded updater).

Fix: release.ps1 copies dist/updater.exe to build/staging/ after
the updater build, and main.spec datas references that staged path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

core/version.py

@@ -4,4 +4,4 @@
 릴리스 시 이 값을 올린 후 git tag → push.
 CHANGELOG.md의 최상단 항목과 일치시킬 것.
 """
-__version__ = '2.2.2'
+__version__ = '2.2.3'