fix(approval): route fallback input() through prompt_toolkit run_in_terminal to fix deadlock

[Feranmi10]

What does this PR do?

Fixes the deadlock in tools/approval.py where get_input was called from a background thread while prompt_toolkit's Application.run() was already running on MainThread. Both competed for stdin, causing the approval prompt to freeze with no way to type o/s/d.

Root cause: In subagent/delegate threads, _callback_tls.approval is None because TLS doesn't propagate to child threads. This caused prompt_dangerous_approval to fall through to its raw input() fallback — which deadlocked with prompt_toolkit's own stdin reader.

Fix — two changes in tools/approval.py:

1. New _try_pt_run_in_terminal(func, timeout) helper that detects a live prompt_toolkit Application via _current_app ContextVar, schedules an async _schedule() coroutine via asyncio.run_coroutine_threadsafe, then inside _schedule, calls app.run_in_terminal(func) — the non-executor path that detaches prompt_toolkit's stdin reader and restores cooked mode before calling func, eliminating the stdin race.
2. Refactored prompt_dangerous_approval fallback to call _try_pt_run_in_terminal first; falls back to the original daemon-thread + input() approach only when None is returned (no live Application — non-TUI paths, tests, cron).

Related Issue

Fixes #15216

Type of Change

• Bug fix