Alt+key combinations for special characters broken on non-US keyboard layouts (Terminal.app, macOS)

### 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 26.5.0 (25F71)

### Expected behaviour

Opening a new panel in Terminal.app, ~ character must be written correctly with the option "Use Option as Meta key" enabled

### Actual behaviour

Since migrating from v2.x to v3.x (2.10.0), Alt+5 no longer produces ~ on Italian keyboard layout in Terminal.app.
The stdin buffer in tui.js converts single bytes >127 to ESC+char sequences, which conflicts with "Use Option as Meta key" enabled. This worked correctly in v2.x. Affects all Alt-composed characters on non-US layouts.

### Steps to reproduce

Activate "Use Option as Meta key" option in the Terminal app, and try to type the ~ character with Alt+5 (external keyboard) or Option+5.
The terminal will refuse the digit.

### Environment

```yaml

[q-details]
version = "2.10.0"
hash = "a5da029503141c8033a11d7ee6569583d915cd90"
date = "2026-06-25T20:10:07.272812Z (15d ago)"
variant = "full"

[system-info]
os = "macOS 26.5.0 (25F71)"
chip = "Apple M4"
total-cores = 10
memory = "16.00 GB"

[environment]
cwd = "/Users/USER"
cli-path = "/Users/USER"
os = "Mac"
shell-path = "/bin/zsh"
shell-version = "5.9"
terminal = "macOS"
install-method = "unknown"

[env-vars]
PATH = "/Users/USER/.nvm/versions/node/v12.22.12/bin:/Users/USER/.local/bin:/Users/USER/.jenv/shims:/Users/USER/.jenv/bin:/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:/pkg/env/global/bin:/Applications/CyberArk EPM.app/Contents/MacOS:/opt/podman/bin:/Users/USER/.local/bin"
QTERM_SESSION_ID = "3f2eddd83a0b4f4b905a502464d67ac2"
Q_SET_PARENT_CHECK = "1"
Q_TERM = "2.10.0"
SHELL = "/bin/zsh"
TERM = "xterm-256color"
__CFBundleIdentifier = "com.apple.Terminal"
```

Inizia in tui.js, nella gestione del buffer stdin descritta nel report, e confronta il suo comportamento con v2.x. Riproduci il problema in Terminal.app con un layout di tastiera italiano e l’opzione “Use Option as Meta key” abilitata; il lavoro è completato quando Alt+5 produce ~ e gli altri caratteri composti con Alt funzionano correttamente.

Scritto dal modello di indicizzazione a partire dal testo della issue.