fix(mobile): take-control tap leaks to xterm on iOS, opens keyboard

[attson]

Repro

On iOS, when the desktop is the active driver and the phone is viewing, the mobile view shows a "远端正在控制 / 接管控制" overlay. Tapping "接管控制" doesn't take control — the on-screen keyboard pops up instead and the overlay stays visible.

Root cause

The take-control button is inside `.viewer-overlay`, a sibling of `.term`. xterm hosts a hidden `<textarea>` (the helper textarea for IME) inside `.term`. On a fast (LAN) relay the sub-100ms roundtrip from `claim_driver` to the broadcast driver-change can land between iOS's `touchstart` and the synthesized click event:

1. touchstart on the button
2. `claimDriver()` fires from a non-click path, or the click handler fires
3. Relay broadcasts driver-change → `isDriver=true` → overlay is removed from DOM
4. iOS synthesizes the click at the touch location, which is now on `.term` / `.xterm` / the helper textarea — focusing it and opening the keyboard

Even when the click does hit the button correctly, the same shape of redirection can mis-fire if the underlying element changes mid-touch.

Fix

Set `.term { pointer-events: none }` whenever `!isDriver`, so the only interactive surface under the touch is the overlay itself. The button can fire its click reliably; the xterm textarea is never reachable while the overlay is up.

Defense-in-depth on the button:

• `type="button"` (was implicit-but-correct; pinned explicitly so future `` wraps don't accidentally make it submit)
• `@click.stop` so the click event can never bubble to a delegated handler on a parent

Test plan

• new vitest case asserts `.term` gets the `inert` class while `!isDriver` and loses it when driver
• existing `shows viewer overlay when not driver; take-control calls claimDriver` test still passes
• `npm test` — 73 files / 615 tests green
• `npx vue-tsc --noEmit` — clean
• manual: on iOS Safari / Capacitor build, with desktop driving and phone viewing, tap "接管控制" — the overlay should disappear and no keyboard pops up