Extend proxy-status with watch mode and notifications

[xodapi]

Why

proxy-status now provides one-shot human/compact/JSON output. The next useful step, borrowed from the limit-watch workflow, is a watch mode and optional local notifications for status transitions.

Scope

• proxy-status --watch <seconds>.
• Optional --notify for transition to limited/error.
• Avoid repeated notification spam for the same state.
• Keep output privacy-safe.

Acceptance criteria

• Watch mode refreshes without memory growth.
• Notification state de-duplicates repeated alerts.
• Works on Windows with a graceful fallback if notification APIs are unavailable.