Move the capture/encode/send pipeline out of cmd/teleportfling into a
GUI-free Engine so the CLI and the desktop app share one implementation:
- flinger: Config/Engine/Status, audio+video+stats loops, pattern source
- config: JSON persistence at ~/.config/teleportfling/config.json
- cmd/teleportfling: thin CLI wrapper around the engine (same flags)
- golangci: extend exclusions to flinger/config
