fix: use TUI account notifications

[davidprokopec]

Summary

• replace synthetic session messages with real TUI switch toasts
• add /chatgpt-pool account management through the package ./tui entrypoint
• serialize server/TUI pool mutations with an owner-fenced interprocess lock
• preserve switch events in an ordered token-free queue

Verification

• bun run check (26 tests)
• concurrent two-store mutation test with dead-owner recovery
• npm pack --dry-run --json includes src/tui.ts and src/notice.ts