fix(macos): open surviving inbox context for ended agents

[jiunbae]

Summary

• resolve Operator Inbox targets by stable agent identity before weaker context fallbacks
• open a surviving window, session, or host when the original live agent ended
• label the action as Open Agent, Open Window, Open Session, or Open Host

Test plan

• xcodebuild -project apps/muxa-macos/Muxa.xcodeproj -scheme Muxa -configuration Debug -destination platform=macOS test (37 passed)
• Release app build and smoke test
• Verified the real rtzr @claude request falls back to its surviving callabo session
• Installed and launched the updated Release app locally