station: Default device type to "unknown" and propagate DHCP hostname

GuessDeviceType silently returned "mobile" for any device whose hostname
or MAC OUI didn't match a known pattern, so the UI labelled every
unidentified device as a phone. Default to "unknown" instead and broaden
hostname matching (pixel/galaxy, thinkpad, imac/-pc, QEMU OUI).

The hostapd backend was also dropping DHCP hostnames on the floor: the
correlator only forwarded MAC->IP, and convertStation hard-coded the
hostname to "". Replace UpdateIPMapping with UpdateLeaseInfo that carries
both maps so hostnames flow through to ConnectedDevice.Name.

Frontend gains a "Sans nom" fallback when no hostname is available and
French labels for the device-type badge.

cmd/repeater/static/app.js

@@ -401,13 +401,17 @@ function displayDevices(devices) {
         const deviceCard = document.createElement('div');
         deviceCard.className = 'device-card';
 
+        const displayName = device.name && device.name.trim() !== ''
+            ? device.name
+            : 'Sans nom';
+
         deviceCard.innerHTML = `
             ${getDeviceIcon(device.type)}
-            <div class="device-name">${escapeHtml(device.name)}</div>
-            <div class="device-type">${device.type}</div>
+            <div class="device-name">${escapeHtml(displayName)}</div>
+            <div class="device-type">${escapeHtml(formatDeviceType(device.type))}</div>
             <div class="device-info">
-                <div>${device.ip}</div>
-                <div style="font-size: 0.75rem;">${device.mac}</div>
+                <div>${escapeHtml(device.ip || '—')}</div>
+                <div style="font-size: 0.75rem;">${escapeHtml(device.mac)}</div>
             </div>
         `;
 
@@ -415,6 +419,17 @@ function displayDevices(devices) {
     });
 }
 
+function formatDeviceType(type) {
+    const labels = {
+        mobile: 'Mobile',
+        tablet: 'Tablette',
+        laptop: 'Portable',
+        desktop: 'Ordinateur',
+        unknown: 'Inconnu'
+    };
+    return labels[type] || labels.unknown;
+}
+
 function addLogEntry(log) {
     const logContainer = document.getElementById('logContainer');