fix(tui): show all submit keybindings in dialog prompt hint bar

[ariane-emory]

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

fix(tui): show all submit keybindings in dialog prompt hint bar

Summary

The dialog prompt hint bar (e.g. Rename Session) only displayed the first
input.submit keybinding instead of all of them. With
input_submit: "shift+return,ctrl+return,alt+return", the hint showed only
shift+enter.

Changes

• keymap.tsx — Added useCommandShortcuts hook that returns all
  registered bindings for a command (vs useCommandShortcut which returns
  only [0]). Also added enter: "return" to keyNameAliases so the
  display matches the user's config key names.
• dialog-prompt.tsx — Replaced useCommandShortcut with
  useCommandShortcuts and joined all bindings with / in the hint bar
  (e.g. shift+return/ctrl+return/alt+return submit).

Test plan

• Open a dialog prompt (e.g. Rename Session via session.rename)
• Confirm the hint bar shows all submit keybindings, not just one
• Confirm key names display as return (not enter)
• Confirm each binding still submits the dialog when pressed