station: Identify devices by MAC OUI vendor lookup

Embed the IEEE OUI registry (~1MB pre-processed text file) and resolve
the vendor for every station MAC. Locally administered MACs (U/L bit
set, used by iOS/Android private addresses and virtual interfaces) are
skipped so we don't return spurious matches against randomized prefixes.

The vendor name shows up in the device card as a secondary line, and
falls back to the title position when no DHCP hostname is available —
"Apple" with the IP and MAC is far more useful than "Sans nom".

The lookup table loads lazily (sync.Once) on the first call so the
~40k-entry parse only runs when the station discovery code is exercised.

cmd/repeater/static/app.js

@@ -403,14 +403,16 @@ function displayDevices(devices) {
 
         const displayName = device.name && device.name.trim() !== ''
             ? device.name
-            : 'Sans nom';
+            : (device.vendor ? device.vendor : 'Sans nom');
 
+        const showVendor = device.vendor && device.vendor !== displayName;
         const metrics = buildDeviceMetrics(device);
 
         deviceCard.innerHTML = `
             ${getDeviceIcon(device.type)}
             <div class="device-name">${escapeHtml(displayName)}</div>
             <div class="device-type">${escapeHtml(formatDeviceType(device.type))}</div>
+            ${showVendor ? `<div class="device-vendor">${escapeHtml(device.vendor)}</div>` : ''}
             <div class="device-info">
                 <div>${escapeHtml(device.ip || '—')}</div>
                 <div class="device-mac">${escapeHtml(device.mac)}</div>

cmd/repeater/static/style.css

@@ -553,7 +553,16 @@ body {
     color: var(--text-tertiary);
     text-transform: uppercase;
     letter-spacing: 0.06em;
+    margin-bottom: 0.125rem;
+}
+
+.device-vendor {
+    font-size: 0.75rem;
+    color: var(--text-secondary);
     margin-bottom: 0.375rem;
+    overflow: hidden;
+    text-overflow: ellipsis;
+    white-space: nowrap;
 }
 
 .device-info {