tui: terminals picker — clearer two-line rows + Delete to close ...

- Each terminal row is now two lines: the name (bold, with status icon) on
  top, the description + pid + uptime as a dim meta line beneath, separated
  by '·' — easier to scan than a single run-on line.
- Close is bound to Delete/Backspace instead of Enter: Enter commonly means
  "open/select", Delete means "remove/close", which matches closing a
  terminal. Title updated: "Open terminals — Delete to close, Esc to cancel".
  No-op on an empty list.

Tests: close-on-delete (was close-on-enter), empty-list delete is a no-op.
Full suite: 1000 passed, 1 skipped.

tui: /terminals command + modal to view and force-close terminals (Etap 5) ...

The final piece of the terminals plan: a modal to list the session's open
persistent terminals and force-close one.

- screens/terminals_picker.py: a modal (mirror of sessions_picker). Seeds the
  list from api.list_terminals on open, kept live by refresh_from_model — the
  app calls it as terminal_opened/closed events arrive while the modal is open
  (closed ones drop out, newly opened append). Each row shows status emoji +
  name (bold) + description + pid + uptime. Up/Down navigate, Enter force-closes
  the highlighted terminal via api.close_terminal (in a worker), Escape cancels.
  Empty list is a no-op for Enter (no crash, no close call).
- commands/builtin.py: TerminalsCommand (/terminals) opens the picker for the
  active session. Registered in the command registry.
- tui_app._open_terminals_picker pushes the screen; on_ws_event's terminal
  branch now also refreshes the picker live if it is the active screen.

Tests: list seed, Enter closes the highlighted terminal (api.close_terminal
called, drops from list), Escape cancels (dismiss None), live refresh filters
closed + adds opened, empty list Enter is a no-op. Input-box hint tests
adjusted for the new /t match order (terminals, thinking, themes). Full suite:
993 passed, 1 skipped.

Plan docs/terminal_tool_plan.md — Etap 5 of 5 (complete).