refactor: move backend options into backend_config section

- 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

monitor-lets-go.example.yaml

@@ -15,10 +15,12 @@ poll_interval: 5s
 # Whether to restore the portable layout when the daemon shuts down.
 restore_on_exit: true
 
-# Optional: override where the generated Hyprland monitor config is written.
-# Supports ~ for home directory expansion.
-# Defaults to ~/.config/hypr/monitors.conf.
-# output_path: ~/.config/hypr/custom-monitors.conf
+# Backend-specific options. Keys depend on the selected backend.
+# Hyprland supports:
+#   output_path — path to the generated monitor config file
+#                 (default: ~/.config/hypr/monitors.conf)
+# backend_config:
+#   output_path: ~/.config/hypr/custom-monitors.conf
 
 # External monitors that trigger docked mode.
 #   Plain name: matches the connector name (e.g. DP-1, HDMI-A-1).