#90: Soft apply remount without rebuild

[Unthred]

Closes #90

Summary

• Separate cold StartAsync (startup build) from RemountWithoutBuildAsync (Settings HardRestart)
• Settings Save is never a build trigger; StartOnLaunch applies to cold BM startup only
• Affected-project remount plans so unrelated Local projects are not bounced
• AI Controlled Hard remounts compile 0 times even when StartOnLaunch is true
• Docs updated for StartOnLaunch / HardRestart remount semantics

Test plan

• Focused SettingsApplyImpact / remount / BuildTrigger / WatchIgnore tests (129)
• Full ship-check (700)
• Manual: WatchExcludeSegments / RunMode / active toggle remount with no build (see PR comment checklist)