[Feature] aac listen — allow presetting auto-approval duration via CLI flag or accept typed input in TUI

# [Feature] `aac listen` — allow presetting auto-approval duration via CLI flag or accept typed input in TUI

## Problem

The `aac listen` TUI (`CredentialConfirm` mode) only accepts `Up` / `Down` arrow keys for the auto-approval timer:

- `Up` = +5 minutes
- `Down` = -1 minute (floor 1)
- Default = 10 minutes (hardcoded at `auto_approve_minutes: 10` in `crates/ap-cli/src/command/tui.rs`)

Digits (0-9), PageUp/PageDown, and Home/End are not bound to the timer field.

## Use case

Persistent `aac listen --reusable-psk` sessions on unattended-cron hosts (e.g., a Mac mini serving multi-day AI-agent workloads while the operator is away) need multi-thousand-minute auto-approval windows so the listener doesn't lapse mid-window.

Reaching a value like **4000 minutes from the default 10 requires ~798 Up-arrow presses**, which is untenable ergonomically.

## Proposed alternatives (any one would solve it)

1. **CLI flag on `listen`:**
```
aac listen --reusable-psk --default-auto-approve-minutes 4000
```
Sets the initial TUI value; user can still adjust with arrows before pressing `a`.

2. **Typed-digit input in the TUI's `CredentialConfirm` mode** — capture `KeyCode::Char(c)` where c is 0-9 into a temporary buffer; commit on Enter.

3. **PageUp/PageDown bindings for coarse stepping** (e.g., ±60min) — cheapest option; keeps the arrow-key UX pattern.

4. **Env-var override:**
```
AAC_DEFAULT_AUTO_APPROVE_MINUTES=4000 aac listen ...
```

Any single one solves the ergonomic problem. Options (1) and (4) are the smallest surface changes.

## Relevant files

- `crates/ap-cli/src/command/listen.rs` — `ListenArgs` struct (add flag here for option 1)
- `crates/ap-cli/src/command/tui.rs` — `CredentialConfirm` key handler (add digit or PageUp/Down bindings for options 2/3)

## Willing to contribute

Yes — happy to submit a PR if maintainers agree on which of (1)–(4) fits the project's design direction.

Start with ListenArgs in crates/ap-cli/src/command/listen.rs and the CredentialConfirm key handler in crates/ap-cli/src/command/tui.rs. Confirm with maintainers which proposed input method fits the design direction, then verify that the chosen method allows a large initial auto-approval duration while preserving adjustment before approval.

Written by the indexing model from the issue text.