- Add bot_bottle/cli/tui.py: curses filter-select picker that opens
/dev/tty directly so it works with redirected stdout/stdin
- Make `name` positional optional (nargs="?") in cmd_start; show agent
picker when absent
- Show backend picker when no --backend flag and BOT_BOTTLE_BACKEND is
unset; skip when either is explicit or the env var is present
- Add tests/unit/test_cli_tui.py covering _filter_items logic and
short-circuit paths (empty list, unavailable tty)
- Add tests/unit/test_cli_start_selector.py covering all four dispatch
combinations (both explicit, agent-absent, backend-absent, both-absent)
and cancel semantics
- Activate PRD 0051
