Alt+Enter keyboard shortcut for multi-line input not working despite being documented

### Checks

- [x] I have searched [github.com/aws/amazon-q-developer-cli/issues](https://github.com/aws/amazon-q-developer-cli/issues?q=) and there are no duplicates of my issue
- [x] I have run `q doctor` in the affected terminal session
- [x] I have run `q restart` and replicated the issue again

### Operating system

macOS 15.6.0 (24G84)

### Expected behaviour

According to the help text displayed by 'q chat', Alt+Enter should work as an alternative to Ctrl+J for inserting new-lines to provide multi-line prompts. The help shows:

"Ctrl(^) + j Insert new-line to provide multi-line prompt
Alternatively, [Alt(⌥) + Enter(⏎)]"

### Actual behaviour

Alt+Enter does not work for multi-line input. Only Ctrl+J works as expected.

### Steps to reproduce

1. Run 'q chat' command
2. Try to use Alt+Enter to create a multi-line prompt
3. Observe that Alt+Enter does not insert a new line
4. Compare with Ctrl+J which works as expected

### Environment

```yaml
[q-details]
version = "1.13.1"
hash = "c658e9e187b6264a24821db3a3ddc591e3095d2f"
date = "2025-08-01T22:08:19.279481Z (7d ago)"

[system-info]
os = "macOS 15.6.0 (24G84)"
chip = "Apple M1 Pro"
total-cores = 10
memory = "32.00 GB"

[environment]
cwd = "/private/tmp"
cli-path = "/private/tmp"
install-method = "brew"

[env-vars]
PATH = "/opt/homebrew/bin:/opt/homebrew/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/usr/local/go/bin:/Applications/iTerm.app/Contents/Resources/utilities:/Users/USER/.local/bin:/Users/USER/bin"
QTERM_SESSION_ID = "3138a1b88a124d1caf04d38f9b6c624c"
Q_SET_PARENT_CHECK = "1"
Q_TERM = "1.12.2"
SHELL = "/opt/homebrew/bin/bash"
TERM = "xterm-256color"
__CFBundleIdentifier = "com.googlecode.iterm2"

[chat-settings]

[chat-trusted_tools]
fs_read=trusted

[chat-failed_request_ids]
none

[chat-context]
current_profile=q_cli_default
profile_context=
AmazonQ.md
README.md
.amazonq/rules/**/*.md

files=none
```