fix(windows): harden installer runtime activation

[uvwt]

Summary

• make fresh Windows installs default to standard user mode while preserving existing privilege mode on upgrades
• split installer provisioning from immediate runtime activation so broker / Task Scheduler activation failures can defer safely on fresh standard installs instead of rolling back a valid install
• improve early ResultFile diagnostics, elevated task rollback recovery, and multi-warning reporting
• add Windows fault-injection coverage for deferred activation and wire it into the installer workflow

Validation

• Windows PowerShell 5.1 installer validation passed
• go test ./scripts/test/... passed
• go test ./... passed
• fresh + standard Setup broker failure injection passed without rollback
• Inno Setup 6.7.3 offline AMD64 installer compiled successfully
• agy final review: no Blocker / High / Medium findings