Add client eviction feature

- Add EvictClient method to DHCP Server
- Add /api/dhcp/leases/evict endpoint to force client IP release
- Add 'Evict' button in Web UI for online clients
- Update table layout to include Action column
- Evicted client will be forced to get a new IP on next DHCP request

internal/dhcp/server.go

@@ -700,3 +700,26 @@ func newBroadcastUDPConn(host string, port int) (*net.UDPConn, error) {
 
 	return udpConn, nil
 }
+
+// EvictClient removes a client's lease, forcing them to get a new IP
+func (s *Server) EvictClient(mac string) error {
+	s.leaseMutex.Lock()
+	defer s.leaseMutex.Unlock()
+
+	lease, exists := s.leases[mac]
+	if !exists {
+		return fmt.Errorf("lease not found for MAC %s", mac)
+	}
+
+	// Remove from in-memory lease map
+	delete(s.leases, mac)
+	delete(s.usedIPs, lease.IP)
+
+	// Delete from database
+	if err := s.db.Where("mac = ?", mac).Delete(&db.DHCPLease{}).Error; err != nil {
+		return fmt.Errorf("failed to delete lease from database: %v", err)
+	}
+
+	log.Printf("DHCP: Evicted client %s (%s)", mac, lease.IP)
+	return nil
+}

internal/web/server.go

@@ -117,6 +117,7 @@ func (s *Server) setupRoutes() {
 		protected.GET("/dhcp/bindings", s.handleGetBindings)
 		protected.POST("/dhcp/bindings", s.handleCreateBinding)
 		protected.DELETE("/dhcp/bindings/:id", s.handleDeleteBinding)
+		protected.POST("/dhcp/leases/evict", s.handleEvictClient)
 		
 		// DNS
 		protected.GET("/dns/config", s.handleGetDNSConfig)
@@ -282,6 +283,30 @@ func (s *Server) handleDeleteBinding(c *gin.Context) {
 	c.JSON(http.StatusOK, gin.H{"message": "Binding deleted"})
 }
 
+func (s *Server) handleEvictClient(c *gin.Context) {
+	var req struct {
+		MAC string `json:"mac"`
+		IP  string `json:"ip"`
+	}
+	
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+	
+	if req.MAC == "" {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "MAC is required"})
+		return
+	}
+	
+	if err := s.dhcpServer.EvictClient(req.MAC); err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+	
+	c.JSON(http.StatusOK, gin.H{"message": "Client evicted successfully"})
+}
+
 func (s *Server) handleGetRecords(c *gin.Context) {
 	records, err := s.dnsServer.GetDNSRecords()
 	if err != nil {