refactor(cli): move update checks to TUI clients

[jlongster]

Summary

• remove automatic update monitoring, Session-idle coordination, event publication, and replacement spawning from background servers
• have every TUI-hosting CLI check immediately and every 10 minutes
• notify the TUI through a same-process CLI callback rather than the server event bus
• show one centered Update / Skip dialog per version
• install only after the user chooses Update; restart only a CLI-managed server
• simplify update policy to update: "disable" | "notify", defaulting to notify
• map retained V1 autoupdate: true and previous V2 update: "auto" to notify
• keep update monitoring cancellation-safe and prevent async completion from closing unrelated dialogs

Testing

• 30 focused CLI updater/install/monitor tests
• standalone upgrade help test passes when run independently (combined run exceeded its existing five-second timeout)
• 4 focused Core config migration/loading tests
• Server process test
• focused TUI app lifecycle test
• Protocol and Website generated-file checks
• git diff --check
• typecheck not run locally per request