Embed updater.exe into main.exe (single-file deployment)

- main.spec: include dist/updater.exe in datas (when present)
- main.py: extract embedded updater.exe next to main.exe on launch
- updater_client.py: _MEIPASS fallback to TEMP if extraction fails
- release.ps1: build updater FIRST so main.spec can embed it

Now users can deploy main.exe alone; auto-update still works because
main.exe self-extracts updater.exe on first launch.

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__ = '2.2.0'
+__version__ = '2.2.1'