Update WebGPU backend to current wgpu/winit APIs

[mors119]

Summary

The current bracket-terminal WebGPU backend does not compile with the dependency versions currently declared in this repository.

Problem

Running:

cargo check -p bracket-terminal --no-default-features --features webgpu

results in compilation failures caused by API incompatibilities between the current implementation and the versions of wgpu/winit used by the workspace.

This affects contributors who want to:

• build with --features webgpu
• maintain or debug the WebGPU backend
• develop or verify WebGPU examples

Proposed solution

Update the WebGPU backend implementation to match the currently used dependency APIs.

Potentially affected areas include:

• WebGPU initialization and device/surface creation
• render pipeline and render pass configuration
• texture upload paths
• framebuffer and sampler configuration
• event/input handling for the WebGPU backend

Alternatives considered

• Downgrade dependencies to match the existing implementation
• Leave the WebGPU backend unsupported

Additional context

This issue is intended to track the current incompatibility and discuss a path toward restoring WebGPU support.