Upgrades bevy_nokhwa to Bevy 0.19.

Highlights

• Bevy 0.16.0-rc.2 → 0.19 — migrates the background renderer off the removed node/edge render graph to Bevy's new camera-driven Core2d/Core3d schedules.
• The background render pipeline is now a SpecializedRenderPipeline keyed on the view's output format (ExtractedView::target_format) and MSAA sample count (Msaa::samples()), compiled asynchronously through the PipelineCache. This fixes a wgpu "Incompatible sample count" validation error that occurs when MSAA is enabled (Bevy's default).
• The webcam shader is now loaded as an embedded asset (embedded_asset! / load_embedded_asset!), enabling hot reloading.
• bevy_egui updated to the published 0.40.

Verified

Ran on a MacBook Pro (Apple Silicon): the camera opens via BackgroundCamera::auto() and the background renders with zero wgpu validation errors.

Breaking / Notes

• Examples switched to BackgroundCamera::auto(). Fixed MJPEG 640x480@30 is rejected by some devices (e.g. Apple Silicon cameras) with "Cannot fulfill request".
• Minimum supported Bevy: 0.19.

Full Changelog: v0.7.0...v0.8.0