Enable mobile emulation

[duncan-bayne]

🚨 Needs rubycdp/ferrum#527 before merging. 🚨

Currently, when creating a Cuprite driver, it's not possible to specify that it should have mobile emulation enabled.

This PR adds that functionality.

Remember to revert 5117a90 once rubycdp/ferrum#527 is merged.

[route]

Notes from reviewing the Ferrum side of this (rubycdp/ferrum#527):

What "mobile emulation" actually is

It's purely a viewport-level concern, made of two independent CDP calls:

1. Emulation.setDeviceMetricsOverride(mobile: true, ...) — makes the page honor <meta name="viewport"> the way a real mobile browser does.
2. Emulation.setTouchEmulationEnabled(enabled: true, ...) — touch events / navigator.maxTouchPoints.

Neither of those needs a specific device size or a mobile User-Agent to work — those are separate, optional pieces (which is exactly what Devices::IPHONE_14 in this PR bundles on the Cuprite side).

What changed on the Ferrum side (and why)

Ferrum::Page#set_viewport(mobile:) already did (1); rubycdp/ferrum#527 originally added (2) to set_viewport too, which is correct — but it also threaded mobile: through Page#resize, which is not correct: resize is Capybara's generic window-resize hook (resize_window_to), unrelated to device emulation. Coupling the two caused a real bug: resize(width: 0, height: 0, mobile: true) forwarded the 0s straight into Browser.setWindowBounds, which (unlike the CDP viewport override) doesn't treat 0 as "leave this alone" — so enabling mobile emulation without a size preset was silently shrinking the actual browser window.

Rather than patching that bug in resize, I removed mobile: from resize entirely and left set_viewport as the sole mobile/touch entry point: https://github.com/rubycdp/ferrum/tree/mobile-emulation-527.
(#527 itself is stale/CONFLICTING against current main)

What this means for this PR

lib/capybara/cuprite/page.rb currently does:

width, height = @options.window_size
resize(width: width, height: height, mobile: @options.mobile)

This will break against the updated Ferrum API (resize no longer accepts mobile:). It needs to become something like:

width, height = @options.window_size
resize(width: width, height: height)
set_viewport(width: width, height: height, mobile: @options.mobile) if @options.mobile

Everything else in this PR (Devices::IPHONE_14, the mobile spec page/driver registration) looks right as-is and doesn't need to change.