T-19: Extend reopenLastProject to reopenAllWindows

[kirich1409]

Part of EPIC #193. Depends on #201.

Description

The current reopenLastProject: Bool setting (from #164) reopens a single project. Extend it to an enum { off, lastProject, allWindows }. In allWindows mode, save the list of open ProjectIDs on quit into @AppStorage and reopen them all via openWindow(value:) on launch. Migration for existing users: old true → .lastProject, old false → .off.

Acceptance Criteria

• Settings pane exposes a picker "Reopen on launch: Off / Last project / All windows"
• Boolean → enum migration preserves the user's prior preference
• In allWindows mode, on quit the open ProjectID list is saved; on launch all windows are reopened
• Scene restoration and this setting do not combine to produce duplicate windows

Module / Layer

Relay / AppDelegate + Settings + StartupRouteResolver

Complexity

Medium