feat(handlers): Add helper methods for hybrid SSR

- Add GetPendingRegistrationsData() to DeviceHandler
- Add GetQueueData() to QueueHandler
- Add template types: DeviceData, PendingRegistrationData, ConflictData, QueueItemData
- Add collection types: CollectionData, CollectionDetailData, BookData

All changes are non-breaking and preserve API compatibility

internal/handlers/devices.go

@@ -489,6 +489,31 @@ func (h *DeviceHandler) RejectDevice(c echo.Context) error {
 	})
 }
 
+func (h *DeviceHandler) GetPendingRegistrationsData(c echo.Context) ([]map[string]interface{}, error) {
+	userID := c.Get("user_id").(string)
+	userUUID, err := uuid.Parse(userID)
+	if err != nil {
+		return nil, err
+	}
+
+	registrations := []map[string]interface{}{}
+	for _, reg := range pendingRegistrations {
+		if reg.UserID == userUUID || reg.UserID == (uuid.UUID{}) {
+			registrations = append(registrations, map[string]interface{}{
+				"registration_id":   reg.RegistrationID,
+				"device_name":       reg.DeviceName,
+				"device_type":       reg.DeviceType,
+				"device_identifier": reg.DeviceIdentifier,
+				"expires_at":        reg.ExpiresAt,
+				"created_at":        reg.CreatedAt,
+				"is_approved":       reg.UserID != (uuid.UUID{}),
+			})
+		}
+	}
+
+	return registrations, nil
+}
+
 func (h *DeviceHandler) ListPendingRegistrations(c echo.Context) error {
 	userID := c.Get("user_id").(string)
 	userUUID, err := uuid.Parse(userID)