feat: improve updater flow and release channels

- added dedicated GUI updater executable and integrated launch path from main app

- added stable/beta update channel selection with persisted settings and checker support

- expanded CI/release validation to include updater and full test discovery

.gitea/workflows/release.yml

@@ -70,8 +70,8 @@ jobs:
         if: env.CONTINUE == 'true'
         shell: powershell
         run: |
-          python -m py_compile app_version.py main.py build.py tests/test_auth_relogin_smoke.py
-          python -m unittest tests/test_auth_relogin_smoke.py
+          python -m py_compile app_version.py main.py build.py updater_gui.py tests/test_auth_relogin_smoke.py tests/test_auto_update_service.py tests/test_chat_actions.py tests/test_token_store.py
+          python -m unittest discover -s tests -p "test_*.py" -v
 
       - name: Build release zip
         if: env.CONTINUE == 'true'