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

web/static/js/app.js

@@ -185,6 +185,17 @@ async function loadClients() {
             statusCell.innerHTML = isActive ? '<span class="status-active">● 在线</span>' : '<span class="status-expired">● 已过期</span>';
             row.appendChild(statusCell);
             
+            // Action buttons
+            const actionCell = document.createElement('td');
+            if (isActive) {
+                const evictBtn = document.createElement('button');
+                evictBtn.textContent = '剔除';
+                evictBtn.style.cssText = 'background-color: #f39c12; color: white; border: none; padding: 5px 10px; border-radius: 3px; cursor: pointer; margin-right: 5px;';
+                evictBtn.onclick = () => evictClient(lease.MAC, lease.IP);
+                actionCell.appendChild(evictBtn);
+            }
+            row.appendChild(actionCell);
+            
             tbody.appendChild(row);
         });
         
@@ -502,6 +513,28 @@ async function deleteBinding(id) {
     }
 }
 
+async function evictClient(mac, ip) {
+    if (!confirm(`确定要剔除主机 ${mac} (${ip}) 吗？\n\n主机将被迫释放该 IP 并重新获取。`)) return;
+    
+    try {
+        const response = await fetch(`/api/dhcp/leases/evict`, {
+            method: 'POST',
+            headers: { 'X-Session-ID': sessionId, 'Content-Type': 'application/json' },
+            body: JSON.stringify({ mac, ip })
+        });
+        
+        if (response.ok) {
+            alert('主机已剔除，将重新获取 IP');
+            loadClients();
+        } else {
+            const data = await response.json();
+            alert('剔除失败：' + (data.error || '未知错误'));
+        }
+    } catch (error) {
+        alert('剔除失败：' + error.message);
+    }
+}
+
 // Load DNS Config
 async function loadDNSConfig() {
     try {