fix(windows): harden desktop OAuth startup

[siyuan-123]

Summary

• normalize a pasted /mcp endpoint to its HTTPS origin before desktop OAuth startup
• persist OAuth access-token TTL in the Windows runtime root, including never
• parse UTF-16 Task Scheduler XML and honor the schema default for missing Enabled
• keep the Windows control panel status logic and uninstall cleanup in sync

Verification

• go test ./internal/desktopruntime ./internal/config ./internal/httpx ./internal/auth ./scripts/test
• built the Windows amd64 core and WPF control panel
• verified local/public health, PKCE OAuth, tools/list, and server_info
• verified the installed AgentDock connector from a signed-in ChatGPT web conversation