Handle persistently locked extension directories

[notmike101]

Summary

• fall back to a verified copy-based extension install when Windows keeps the directory locked after retries
• preserve rollback contents and activation verification
• bump host and SDK to 0.3.8

Verification

• bun run check (48 tests plus SDK, example, and Windows binary builds)
• live ZCode 3.5.2 update: Scheduler 0.1.5 -> 0.1.6 applied and pending transaction cleared