Add VLAN overview table to VLAN configuration page

Below the configuration form, a new table lists all configured VLANs
with their port memberships: Member, Tagged, Untagged, and PVID
columns. Port ranges are formatted compactly (e.g. "1-2,5").

Port-to-bit mapping uses the existing physToLogPort[] array populated
by /status.json, so the table is consistent with the icon view in
fetchVLAN() and works on any supported machine.

Each row has a delete button that sends "vlan N d" via /cmd, with
a confirmation dialog. VLAN 1 cannot be deleted (no button shown).

Table and dropdown both refresh automatically after Update/Create
and after delete via a new refreshVlanViews() helper.

The N+1 request pattern (1x /vlanlist + Nx /vlan.json) keeps the
backend simple and avoids buffer overflow risks for systems with
many VLANs. For typical configurations (<50 VLANs), page load
remains under one second.

html/vlan.html

@@ -36,6 +36,22 @@
       <br/> <input style="width:40%;" class="action" id="vlan_sub" onclick="vlanSub();" type="button" value="Update / Create">
       <script src="/vlan_sub.js"></script>
     </form>
+    <h2>Configured VLANs</h2>
+    <table id="vlanTable" style="width:90%">
+      <thead>
+        <tr>
+          <th>VLAN</th>
+          <th>Name</th>
+          <th>Member Ports</th>
+          <th>Tagged Ports</th>
+          <th>Untagged Ports</th>
+          <th>PVID Ports</th>
+          <th>Delete</th>
+        </tr>
+      </thead>
+      <tbody id="vlanTableBody">
+      </tbody>
+    </table>
     </div>
     <script src="/navigation.js"></script>
   </body>