Improve simulator recovery diagnostics

[Maples7]

Summary

• clarify vch doctor --json stale-prune semantics with worktreePruneRan while keeping prunedStaleEntries as a deprecated compatibility field
• include an explicit stale simulator binding repair hint in doctor human and JSON output
• detect SBMainWorkspace Busy / Application failed preflight checks xcodebuild logs and print recovery commands for --erase-clone or vch sim erase
• add Core unit coverage plus CLI smoke coverage for stderr routing and doctor JSON schema

Refs #118

Tests

• swift test --filter 'VchCLISmokeTests.testTestPreflightBusyFailurePrintsRecoveryHintOnStderr|VchCLISmokeTests.testDoctorJSONReportsWorktreePruneAndStaleBindingHint'
• swift test --parallel