Add WLED auto-discovery via mDNS with zeroconf

Scan the local network for WLED devices advertising _wled._tcp.local.
and present them in the Add Device modal for one-click selection.

- New discovery.py: async mDNS browse + parallel /json/info enrichment
- GET /api/v1/devices/discover endpoint with already_added dedup
- Header scan button (magnifying glass icon) in add-device modal
- Discovered devices show name, IP, LED count, version; click to fill form
- en/ru locale strings for discovery UI

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/static/app.js

@@ -879,6 +879,16 @@ function showAddDevice() {
     const error = document.getElementById('add-device-error');
     form.reset();
     error.style.display = 'none';
+    // Reset discovery section
+    const section = document.getElementById('discovery-section');
+    if (section) {
+        section.style.display = 'none';
+        document.getElementById('discovery-list').innerHTML = '';
+        document.getElementById('discovery-empty').style.display = 'none';
+        document.getElementById('discovery-loading').style.display = 'none';
+    }
+    const scanBtn = document.getElementById('scan-network-btn');
+    if (scanBtn) scanBtn.disabled = false;
     modal.style.display = 'flex';
     lockBody();
     setTimeout(() => document.getElementById('device-name').focus(), 100);
@@ -890,6 +900,79 @@ function closeAddDeviceModal() {
     unlockBody();
 }
 
+async function scanForDevices() {
+    const loading = document.getElementById('discovery-loading');
+    const list = document.getElementById('discovery-list');
+    const empty = document.getElementById('discovery-empty');
+    const section = document.getElementById('discovery-section');
+    const scanBtn = document.getElementById('scan-network-btn');
+
+    section.style.display = 'block';
+    loading.style.display = 'flex';
+    list.innerHTML = '';
+    empty.style.display = 'none';
+    if (scanBtn) scanBtn.disabled = true;
+
+    try {
+        const response = await fetch(`${API_BASE}/devices/discover?timeout=3`, {
+            headers: getHeaders()
+        });
+
+        if (response.status === 401) { handle401Error(); return; }
+
+        loading.style.display = 'none';
+        if (scanBtn) scanBtn.disabled = false;
+
+        if (!response.ok) {
+            empty.style.display = 'block';
+            empty.querySelector('small').textContent = t('device.scan.error');
+            return;
+        }
+
+        const data = await response.json();
+
+        if (data.devices.length === 0) {
+            empty.style.display = 'block';
+            return;
+        }
+
+        data.devices.forEach(device => {
+            const card = document.createElement('div');
+            card.className = 'discovery-item' + (device.already_added ? ' discovery-item--added' : '');
+            const meta = [device.ip];
+            if (device.led_count) meta.push(device.led_count + ' LEDs');
+            if (device.version) meta.push('v' + device.version);
+            card.innerHTML = `
+                <div class="discovery-item-info">
+                    <strong>${escapeHtml(device.name)}</strong>
+                    <small>${escapeHtml(meta.join(' \u00b7 '))}</small>
+                </div>
+                ${device.already_added
+                    ? '<span class="discovery-badge">' + t('device.scan.already_added') + '</span>'
+                    : ''}
+            `;
+            if (!device.already_added) {
+                card.onclick = () => selectDiscoveredDevice(device);
+            }
+            list.appendChild(card);
+        });
+    } catch (err) {
+        loading.style.display = 'none';
+        if (scanBtn) scanBtn.disabled = false;
+        empty.style.display = 'block';
+        empty.querySelector('small').textContent = t('device.scan.error');
+        console.error('Device scan failed:', err);
+    }
+}
+
+function selectDiscoveredDevice(device) {
+    document.getElementById('device-name').value = device.name;
+    document.getElementById('device-url').value = device.url;
+    const typeSelect = document.getElementById('device-type');
+    if (typeSelect) typeSelect.value = device.device_type;
+    showToast(t('device.scan.selected'), 'info');
+}
+
 async function handleAddDevice(event) {
     event.preventDefault();