Add interactive Image Playground flow

[backslash-f]

Summary

• add portable request, concept, availability, and temporary-result values
• wrap the supported SwiftUI Image Playground sheet with completion/cancellation mapping
• keep shared targets buildable on tvOS while reporting generation unavailable
• document the host-owned persistence boundary and add privacy-safe lifecycle logging

Validation

• AgentGuidelines/Scripts/swift_format.sh format-and-lint Package.swift Sources Tests
• swift test
• AgentGuidelines/Scripts/validate_consumer_setup.swift --consumer-root . --require-swift-format
• xcodebuild -scheme ImageForgeKit -destination generic/platform=iOS build CODE_SIGNING_ALLOWED=NO
• xcodebuild -scheme ImageForgeKit -destination generic/platform=tvOS -derivedDataPath /tmp/imageforgekit-tvos build CODE_SIGNING_ALLOWED=NO

Limitations

• physical-device Image Playground acceptance remains for consumer integration; CI cannot exercise the system-managed generation UI