release: TokenStep 0.2.6 update flow

[Backtthefuture]

Summary

• present the update window immediately after a manual check finds a release
• close transient menu-bar panels and foreground the update window
• add installer lifecycle logs and an isolated DMG verification script
• bump release metadata and add 0.2.6 release notes

Validation

• swift test --package-path TokenStepSwift — 100/100 passed
• TOKENSTEP_VERSION=0.2.6 ./script/build_swiftui_and_run.sh --no-launch — passed
• real 0.2.5 DMG signature and isolated install — passed
• live 0.2.4 → 0.2.5 replacement and relaunch — passed