feat: size: prefix, external auto-detection, auto-disable stale monitors

- size:WxH and size:WxH@R resolution for config names
- auto-detection of external monitors when external list is empty (any non-internal display)
- ensureCleanLayout: explicitly disable connected monitors not in target layout
- update docs (README, example.yaml) for all three features

internal/backend/hyprland.go

@@ -92,6 +92,10 @@ func (h *hyprlandBackend) GetMonitors(ctx context.Context) ([]MonitorInfo, error
 
 // ApplyLayout writes the monitor configuration file and calls hyprctl reload.
 // The config is written atomically (temp file + rename) to prevent corruption.
+//
+// Any physically connected monitor not mentioned in the desired layout is
+// explicitly disabled. This prevents external monitors from remaining enabled
+// when switching to portable mode (where only eDP-* is listed).
 func (h *hyprlandBackend) ApplyLayout(ctx context.Context, monitors []MonitorConfig) error {
 	var err error
 	monitors, err = resolveMonitorNames(ctx, monitors, h.GetMonitors, h.logger)
@@ -99,6 +103,14 @@ func (h *hyprlandBackend) ApplyLayout(ctx context.Context, monitors []MonitorCon
 		return fmt.Errorf("resolve monitor names: %w", err)
 	}
 
+	// Fetch the current set of connected monitors and explicitly disable
+	// any that are not part of the target layout.
+	current, err := h.GetMonitors(ctx)
+	if err != nil {
+		return fmt.Errorf("get current monitors for cleanup: %w", err)
+	}
+	monitors = h.ensureCleanLayout(monitors, current)
+
 	content := h.generateConf(monitors)
 
 	destPath, err := h.resolveOutputPath()
@@ -282,6 +294,33 @@ func (h *hyprlandBackend) generateConf(monitors []MonitorConfig) string {
 	return buf.String()
 }
 
+// ensureCleanLayout adds disabled entries for any physically connected
+// monitor that is not present in the target layout. This prevents
+// monitors from remaining enabled when switching to a mode that only
+// configures a subset of displays (e.g. portable mode).
+func (h *hyprlandBackend) ensureCleanLayout(target []MonitorConfig, connected []MonitorInfo) []MonitorConfig {
+	names := make(map[string]bool, len(target))
+	for _, m := range target {
+		names[m.Name] = true
+	}
+
+	var result []MonitorConfig
+	result = append(result, target...)
+
+	for _, mi := range connected {
+		if !names[mi.Name] {
+			h.logger.Debug("explicitly disabling unlisted monitor",
+				"monitor", mi.Name)
+			result = append(result, MonitorConfig{
+				Name:    mi.Name,
+				Enabled: false,
+			})
+		}
+	}
+
+	return result
+}
+
 // formatScale formats a scale float: 1 → "1", 1.5 → "1.5"
 func formatScale(s float64) string {
 	if s == 0 {