Add support for Object Detector models

[JamesDale]

Summary

Adds support for Create ML / Core ML Object Detector models via a new SwiftUI view, ObjectDetectorView.

It runs a VNCoreMLRequest on each live camera frame and publishes the labels of the detected objects (the top label of each VNRecognizedObjectObservation) through a detectedObjects: Binding<[String]>. The design deliberately mirrors the existing model-backed views (ImageClassifierView, HandPoseClassifierView):

• Graceful degradation — a bad/missing model doesn't crash the host app. The camera feed still shows, no detections are produced, the failure is logged via PKLog, and it's reported through the optional onError: ((PrototypeKitError) -> Void)? closure (reusing the existing .modelLoadFailed case).
• Camera selection — accepts an optional camera: CameraOptions?.
• Uses .scaleFill crop/scale so objects near the frame edges aren't discarded (object detectors localize across the whole frame).

Public API

public init(modelURL: URL,
            detectedObjects: Binding<[String]> = .constant([]),
            camera: CameraOptions? = nil,
            onError: ((PrototypeKitError) -> Void)? = nil)

Changes

• New: Sources/PrototypeKit/Public/ObjectDetectorView.swift — the view + ObjectDetectorReceiver.
• New: Tests/PrototypeKitTests/OD/ObjectDetectorTests.swift — view init, onError, and nil-model graceful-failure coverage.
• Tests: extended GracefulFailureTests with the equivalent object-detector cases (bad-URL init, onError, nil-model receiver ignores frames).
• Docs & tooling: README section, DocC topic entry, SKILL.md API reference + camera-view / model-view lists + corrected gotcha, CHANGELOG (Unreleased), Examples gallery entry, a new /prototypekit:object-detector scaffolding command, plugin README table row, and marketplace description.

Testing

⚠️ No Swift toolchain is available in this environment (the package depends on Apple-only frameworks — Vision/CoreML/AVFoundation/SwiftUI — so it builds and tests on macOS CI only). Changes were written to match the established patterns; CI on macOS will exercise the new tests. The receiver/view tests avoid needing a real object-detection model by covering the nil-model and bad-URL paths, consistent with the existing GracefulFailureTests.

🤖 Generated with Claude Code

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