Three bugs fixed in KeyboardHandler:
1. onKeyboardShow() used sessionData.terminal (always undefined) instead of app.terminal
2. Keyboard dismiss threshold (50px) too tight for iOS address bar drift — widened to 100px
3. No terminal refit on keyboard hide — caused black gap below terminal
Also added: dynamic baseline update for initialViewportHeight, safety check in
updateLayoutForKeyboard() that forces dismiss when keyboardOffset <= 0.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
