surface_input drops MouseDownEvent::click_count, so a producer cannot see a double-click #4

Crate: gpui_interop 0.1.3 and 0.2.0 (src/input.rs).

SurfaceEvent::PointerDown carries position, button and modifiers (src/input.rs:124-128), while GPUI's MouseDownEvent also has click_count: usize (bite-gp-types/src/input.rs:83-87) — computed per platform, and by the browser's own time/distance heuristic (bite-gp-web/src/events.rs:128-144).

A CAD consumer needs it: a single click selects a face, a double click opens the feature (FerroCAD's viewport switches on click_count today). Without it, a producer re-implements click counting from timestamps and positions — exactly the kind of platform detail the gateway exists to absorb.

Suggested: add click_count: usize to PointerDown (and consider it on PointerUp for symmetry). One field copied from the event.

We carry this in a vendored copy and use it for double-click-to-recentre.

Status (0.2.0, 2026-11-03): unchanged — src/input.rs is byte-identical
between 0.1.3 and 0.2.0, and the patch described here still applies
unchanged.