Keylight C++ SDK v0.1.0

Added

• JUCE single-header adapter (integrations/juce/KeylightJuce.h):
  keylight::juce_integration::JuceUrlTransport (implements keylight::Transport
  over juce::URL::createInputStream with InputStreamOptions — no OpenSSL,
  no cpp-httplib) and keylight::juce_integration::Licensing (owns the Client,
  FileStore, and transport; exposes activate/validate/deactivate/
  checkOnLaunch with message-thread callbacks via
  juce::MessageManager::callAsync; audio-thread-safe state() and
  hasFeature() via std::atomic snapshots updated by the SDK subscription
  callback; multi-instance safe — no global/static mutable state). Compiles
  against JUCE 7 and JUCE 8 headers with zero extra dependencies beyond
  juce_core. Manual plugin-project build pending: no JUCE toolchain is
  available in CI; a developer with JUCE 7/8 installed must compile and
  smoke-test before shipping.
• Unreal Engine plugin (integrations/unreal/Keylight/): UKeylightSubsystem
  (Blueprint-callable Activate/Validate/Deactivate/HasEntitlement/GetState
  with FOnKeylightResult async delegates), FHttpTransport (UE FHttpModule
  adapter for keylight::Transport — blocks a background thread via FEvent,
  never the game thread), and UELicenseStore (lease persistence under
  Saved/Keylight/). The plugin compiles against UE 5.x headers with zero
  extra dependencies beyond Core, CoreUObject, Engine, HTTP, and Json.
  Manual editor build pending: no UE toolchain is available in CI; a
  developer with UE 5.x installed must compile and smoke-test before shipping.