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

cmd/monitor-lets-go/main.go

@@ -60,7 +60,9 @@ func run(logger *slog.Logger) error {
 	logger.Info("config loaded", "path", configPath, "backend", cfg.Backend)
 
 	// Resolve the backend (auto-detect or explicit).
-	b, err := resolveBackend(cfg.Backend, cfg.OutputPath, logger)
+	// EffectiveBackendConfig merges deprecated top-level keys
+	// into the backend_config map with proper priority.
+	b, err := resolveBackend(cfg.Backend, cfg.EffectiveBackendConfig(), logger)
 	if err != nil {
 		return fmt.Errorf("resolve backend: %w", err)
 	}
@@ -86,11 +88,11 @@ func run(logger *slog.Logger) error {
 // resolveBackend returns the first available backend. When backendName is
 // "auto", backends are probed in priority order. To add a new backend,
 // register it in the backends slice below.
-func resolveBackend(backendName, outputPath string, logger *slog.Logger) (backend.Backend, error) {
+func resolveBackend(backendName string, backendConfig map[string]any, logger *slog.Logger) (backend.Backend, error) {
 	// Ordered by priority: preferred backends first.
 	backends := []struct {
 		name    string
-		factory func(*slog.Logger, string) (backend.Backend, error)
+		factory func(*slog.Logger, map[string]any) (backend.Backend, error)
 	}{
 		{"hyprland", backend.NewHyprland},
 		// Future: {"sway", backend.NewSway},
@@ -99,7 +101,7 @@ func resolveBackend(backendName, outputPath string, logger *slog.Logger) (backen
 
 	if backendName == "auto" {
 		for _, entry := range backends {
-			b, err := entry.factory(logger, outputPath)
+			b, err := entry.factory(logger, backendConfig)
 			if err == nil {
 				logger.Info("auto-detected backend", "name", b.Name())
 				return b, nil
@@ -112,7 +114,7 @@ func resolveBackend(backendName, outputPath string, logger *slog.Logger) (backen
 	// Explicit backend selection.
 	for _, entry := range backends {
 		if entry.name == backendName {
-			b, err := entry.factory(logger, outputPath)
+			b, err := entry.factory(logger, backendConfig)
 			if err != nil {
 				return nil, fmt.Errorf("backend %s: %w", backendName, err)
 			}