ask_user form: pressing Esc silently discards the entire form instead of clearing current input #4943

Describe the bug
When answering an agent-presented form (via the ask_user/elicitation tool), pressing Esc closes/cancels the whole form. Everywhere else in the CLI, Esc clears the current text input (per /help: "esc esc - clear input, interrupt, stop agents, or rewind"). This inconsistency makes it very easy to accidentally lose an entire in-progress form response when the user's intent was just to clear/edit the current field.

Expected behavior
Esc inside a form field should clear that field's current text (consistent with normal prompt behavior), not close/cancel the form. A separate, distinct key/action should be used to actually cancel the form.

Additional context
This came up in a real session: the user had already answered one question in a multi-field form, hit Esc intending to clear/edit text, and the entire form closed with no indication of what (if anything) was preserved. The agent had no way to tell whether the cancellation was intentional or not.