feat: Integrate IProcessInfoProvider IPC into core workflow

[JusterZhu]

Summary

The IProcessInfoProvider abstraction and all 4 implementations (NamedPipe / SharedMemory / EncryptedFile / AutoFallback) are fully implemented, but the core workflow still uses the old Environments.SetEnvironmentVariable("ProcessInfo", ...) approach for Client-to-Upgrade IPC.

Current State

• ClientUpdateStrategy.ExecuteStandardWorkflowAsync() serializes ProcessInfo to Environments
• GeneralUpdateBootstrap.InitializeFromEnvironment() reads via Environments.GetEnvironmentVariable()
• IProcessInfoProvider with NamedPipeProcessInfoProvider, SharedMemoryProcessInfoProvider, EncryptedFileProcessInfoProvider, and AutoProcessInfoProvider are all implemented but unused

Expected

1. Client-side: use AutoProcessInfoProvider.SendAsync() to pass ProcessInfo (auto-fallback: NamedPipe, SharedMemory, EncryptedFile)
2. Upgrade-side: use AutoProcessInfoProvider.ReceiveAsync() to receive ProcessInfo
3. Remove the old Environments usage for ProcessInfo IPC (keep for other env variables if needed)

Benefits

• NamedPipe: zero file residue, most secure
• SharedMemory: Linux-friendly, no fs residue
• EncryptedFile: fallback when pipes/shm unavailable
• Auto-fallback ensures maximum cross-platform compatibility

Ref

Refactoring plan v2: Sub Issue 6 (ProcessInfo IPC re-design)