wterm's iOS Safari compatibility for text input, selection, and pasting.

Hi! Ok in my recent PR for my agent-of-empires project (github.com/njbrake/agent-of-...

I was trying to work through how to handle text selection and pasting from iOS. Do you have any tips or pointers on best practices for wterm on iOS? Here are the couple of issues I found (Claude output after hours of debugging):

## Problem

wterm's InputHandler creates a hidden textarea with styles that prevent it from working correctly on iOS Safari:

### 1. Textarea positioned at -9999px with pointerEvents: none

// input.js, InputHandler constructor
s.left = "-9999px";
s.pointerEvents = "none";

iOS Safari only opens the soft keyboard when a focused input/textarea is within the visual viewport. With left: -9999px, calling textarea.focus() does not open the keyboard. Similarly, pointerEvents: none prevents the textarea from receiving any touch events, making native paste impossible.

Workaround (consumer side): After term.init(), patch the textarea:
const ta = term.element.querySelector("textarea");
ta.style.left = "0";
ta.style.top = "0";
ta.style.pointerEvents = "auto";

Suggested fix: On touch-primary devices (matchMedia('(pointer: coarse)')), position the textarea at 0,0 instead of -9999px and set pointerEvents: auto. The textarea is already invisible via color: transparent; background: transparent; caretColor: transparent, so it won't be visually visible. Alternatively, expose the textarea element publicly so consumers can style it without querySelector hack...