Feat: add persisted account theme settings

Backend/internal/httpx/api_settings_routes.go

@@ -0,0 +1,43 @@
+package httpx
+
+import (
+	"net/http"
+	"strings"
+
+	bootstrapservice "moku-backend/internal/bootstrap"
+)
+
+type saveThemePresetRequest struct {
+	PresetID string `json:"presetId"`
+}
+
+func (routes apiRoutes) handleSaveThemePreset(w http.ResponseWriter, r *http.Request) {
+	payload, ok := decodeBootstrapRequest[saveThemePresetRequest](w, r)
+	if !ok {
+		return
+	}
+
+	payload.PresetID = strings.TrimSpace(payload.PresetID)
+	if payload.PresetID == "" {
+		WriteError(w, http.StatusBadRequest, RequestIDFromContext(r.Context()), "invalid_request", "Theme preset ID is required.")
+		return
+	}
+
+	admin, err := routes.bootstrapService().SaveThemePreset(r.Context(), bootstrapservice.SaveThemePresetInput{
+		PresetID: payload.PresetID,
+	})
+	if err != nil {
+		routes.writeBootstrapPersistenceError(w, r, err)
+		return
+	}
+
+	WriteJSON(w, http.StatusOK, map[string]any{
+		"data": map[string]any{
+			"presetId": payload.PresetID,
+			"admin":    admin,
+		},
+		"meta": map[string]any{
+			"resource": "settings-theme",
+		},
+	})
+}