feat(handlers): implement consolidated user profile endpoints

Implement DeleteUser, ResetUserPassword, and UpdateUserAdmin handlers.
Update collections handler to check soft-deleted users. Update dashboard
service to exclude deleted users from statistics.

internal/handlers/dashboard.go

@@ -103,6 +103,7 @@ func (h *DashboardHandler) RestoreSystemCollection(c echo.Context) error {
 
 	var req struct {
 		CollectionName string `json:"collection_name"`
+		ResetType      string `json:"reset_type"` // "full" or "keep_books"
 	}
 
 	if err := c.Bind(&req); err != nil {
@@ -113,6 +114,10 @@ func (h *DashboardHandler) RestoreSystemCollection(c echo.Context) error {
 		return c.JSON(http.StatusBadRequest, map[string]string{"error": "collection_name required"})
 	}
 
+	if req.ResetType == "" {
+		req.ResetType = "full"
+	}
+
 	validCollections := map[string]bool{
 		"continue-reading": true,
 		"recently-added":   true,
@@ -123,7 +128,11 @@ func (h *DashboardHandler) RestoreSystemCollection(c echo.Context) error {
 		return c.JSON(http.StatusBadRequest, map[string]string{"error": "Invalid system collection name"})
 	}
 
-	err := h.dashboardService.RestoreSystemCollection(c.Request().Context(), userUUID, req.CollectionName)
+	if req.ResetType != "full" && req.ResetType != "keep_books" {
+		return c.JSON(http.StatusBadRequest, map[string]string{"error": "reset_type must be 'full' or 'keep_books'"})
+	}
+
+	err := h.dashboardService.RestoreSystemCollection(c.Request().Context(), userUUID, req.CollectionName, req.ResetType)
 	if err != nil {
 		return c.JSON(http.StatusInternalServerError, map[string]string{"error": "Failed to restore system collection"})
 	}