Extract shared resolveMonitorNames to backend package so both
Hyprland and Sway backends resolve desc: prefixed names to actual
connector names before applying monitor layout.
Previously the Hyprland backend wrote desc:... literally into
monitors.conf, which Hyprland ignores, causing monitors to be
positioned incorrectly or not configured at all.
- Add BackendConfig map[string]any to Config struct
- Deprecate top-level output_path (backward compatible via EffectiveBackendConfig())
- NewHyprland now accepts opts map[string]any instead of raw outputPath
- Factory signature unified to func(*slog.Logger, map[string]any) for all backends
- Update README with backend_config docs and fix Sway skeleton signature
- Update example.yaml to show backend_config instead of output_path
